Inhibition of monoamine oxidase by N-phenacyl-cyclopropylamine

N-phenacyl-cyclopropylamine hydrobromide (54761) was evaluated in vitro and in vivo as a monoamine oxidase (MAO) inhibitor in rats. In contrast to 51641, which has an o-chlorophenoxy group in place of the phenacyl group and which is a highly selective inhibitor of type A MAO, 54761 showed a slight preference as a type B MAO inhibitor, since it inhibited phenylethylamine oxidation at slightly lower concentrations than were required to inhibit serotonin oxidation in vitro by rat liver MAO. Twelve analogs of 54761 with various substituents on the phenyl ring were also studied, but none was substantially more selective than 54761 as a type B inhibitor and most were preferential type A inhibitors. When 51641 and 54761 were injected into rats and MAO activity was assayed in tissue homogenates, the oxidation of serotonin in brain, heart and liver was inhibited more by 51641 than by 54761. In contrast, the oxidation of phenylethylamine was inhibited more by 54761 than by 51641 in brain and liver. In heart, however, 51641 was a more effective inhibitor of phenylethylamine oxidation than was 54761, supporting earlier evidence that phenylethylamine is destroyed in heart mainly by type A MAO. The oxidation of exogenous [¹⁴C]phenylethylamine was inhibited in vivo more effectively by 54761, whereas the oxidation of endogenous serotonin in brain was inhibited more by 51641. Although 54761 is not as selective an inhibitor of type B MAO as some other compounds such as deprenyl, it illustrates that a large range of selectivity in MAO inhibition can exist within the N-cyclopropylamine series. Further, selective type B inhibition could be achieved in vivo 24 hr after injection of 54761 by co-administration of harmaline. Harmaline selectively protected against the inactivation of type A MAO by 54761 but permitted the inactivation of type B MAO to occur.     

The effects of cadmium, manganese and aluminium on sodium-potassium-activated and magnesium-activated adenosine triphosphatase activity and choline uptake in rat brain synaptosomes

The effects of Cd²⁺, Mn²⁺ and Al³⁺ on rat brain synaptosomal sodium-potassium-activated and magnesium-activated adenosine triphosphatase (Na-K-ATPase and Mg-ATPase) activity and choline uptake were studied. All three types of metal ions inhibited Na-K-ATPase activity more markedly than Mg-ATPase activity. The rank order of inhibition of Na-K-ATPase was: $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.4 μ}\text{M}\text{) >}\text{Mn}{}_{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 955 μ}\text{m}\text{) >}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 8.3}\text{mM}$). The rank order of inhibition of Mg- was:$\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 316 μ}\text{M}\text{>}\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 5.5}\text{mM}\text{>}\text{Al}{}^{\mathrm{3+}}\text{(}\text{ic}{}_{50}\text{= 21.9}\text{mM}\text{).}\text{Al}{}^{\mathrm{3+}}$ was most potent in inhibiting synaptosomal choline uptake ($\text{ic}{}_{50}\text{= 24μ}\text{M}$ in the absence of Ca²⁺ and 123 μ.M in the presence of 1 mM Ca²⁺). $\text{Cd}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 363 μ}\text{M}\text{)}$ was a more effective inhibitor of choline uptake than $\text{Mn}{}^{\mathrm{2+}}\text{(}\text{ic}{}_{50}\text{= 1.2?1.5}\text{mM}\text{)}$ . The presence of 1 mM Ca²⁺ did not alter choline uptake, nor did it antagonize the inhibitory actions of the three metals. Our observations that Cd²⁺ and Al³⁺ inhibited synaptosomal choline uptake, but did not show parallel inhibitory effects on Na-K-ATPase activity directly contradicts the ionic gradient hypothesis. These results are also discussed in relation to the in vivo neurotoxicity of cadmium, manganese and aluminium.     

Modulation of cysteine metabolism in mice—Effects of propargylglycine and l-cyst(e)ine-degrading enzymes

In an attempt at evaluating the therapeutic effects of cysteine depletion on the growth of cysteine-dependent L1210 leukemia, the effects in vivo of a cysteine- and cystine-degrading enzyme as well as the combined use of an inhibitor of cysteine biosynthesis with cystine-free diets, were measured in mice. The kinetic properties of rat liver γ-cystathionase (EC 4.2.1.13) and Enterobacter cloacae cysteine desulfhydrase (EC 4.4.1.1) toward the catabolism of cystine and cysteine, as well as the inhibitory properties of some possible physiological components, are described. A novel and sensitive assay for the detection of cysteine in biological fluids was used to measure the ability of these enzymes to deplete plasma cysteine levels when injected into normal mice. Cysteine desulfhydrase caused no alteration in mouse plasma cysteine concentrations, presumably due to rapid clearance ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ less than 10 min) of the enzyme. γ-Cystathionase caused a 60 per cent drop in plasma cysteine concentrations which returned to normal with the clearance of the enzyme ($\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 2}\text{hr}$). The properties and limitations of these enzymes are discussed within the context of their ability to deplete plasma cys(e)ine in vivo. When propargylglycine, an effective covalent inhibitor of γ-cystathionase, both in vitro (K_i = 0.1 mM, saturating $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 0.5}\text{min}$) and in vivo, was combined with diets lacking cystine, no reduction in plasma cysteine or increase in survival of mice bearing L1210 leukemia could be observed. The compound would induce a cystathioninemia and a cystathioninuria when given to mice and was not toxic in cell culture or in animals when tested with an adequate source of cystine, but was highly toxic in the absence of cystine.     

Neuronal and hormonal influences on the turnover of monoamine oxidase in salivary gland

The rate of formation of monoamine oxidase (MAO) in rat submaxillary gland was evaluated from the return of MAO activity after treatment with the irreversible inhibitor drug pargyline. We found that parasympathetic decentralization or sympathetic denervation of the gland had no significant effect on the half-life or the specific activity of the enzyme. The weight of the gland, however, was reduced after both surgical procedures; consequently, the rate of formation of MAO per gland was diminished in direct proportion to the loss of weight. Reserpine treatment, in contrast, had no effect on the weight of the gland, but it increased the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of the enzyme from 3.4 to 5.2 days and decreased its specific activity resulting in a diminuation of the rate of formation of the enzyme. Thyroidectomy had no effect on the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ or the specific activity of the enzyme. Treatment with L-3,3',5-triiodothyronine increased the activity of MAO in the salivary gland of normal and thyroidectomized rats, and it accelerated the return of enzyme activity after pargyline treatment in thyroidectomized animals.     

3H]dihydroergocryptine binding to bovine striatal membranes defined by a low d-butaclamol concentration: antagonism by substituted benzamides

An apparent dopamine-D2 receptor binding system was characterized using [³H]dihydroergocryptine (DHE) as the ligand. Specific binding to bovine striatal membranes was defined as the difference between binding in the absence and in the presence of 4 nM d-butaclamol. These high affinity binding sites (K_d = 0.24 nM) were saturable (B_max = 75 fmoles/mg protein), apparently homogeneous, non-interacting, and stereospecific. Specific binding was greatest in areas rich in dopaminergic innervation. In competition experiments, apomorphine (ic₅₀ = 100 nM) was fifty times more potent than dopamine which, in turn, was nine times more potent than l-norepinephrine and serotonin. Antipsychotic drugs including the substituted benzamides—metoclopramide, sulpiride and sultopride—were active in competing with [³H]DHE for these binding sites ($\text{ic}{}_{50}\text{= 100}\text{nM}$), and their affinities agreed well with their anti-dopaminergic potencies in vivo. Potencies of antipsychotic drugs in competing for DHE binding sites were increased compared to their potencies in competing for [³H]spiroperidol binding sites using 1 μM d-butaclamol as the masking ligand. This relative increase was about 10-fold greater for the substituted benzamides than for other antipsychotic drugs. The relative inactivity of substituted benzamides in competing for binding sites labeled by spiroperidol was accounted for by their greater selectivity for dopamine receptors. In binding studies using a non-selective radio-ligand, selectivity could be enhanced by defining specific binding sites with a low concentration of masking ligand.     

Dopaminergic effects of buspirone,a novel anxiolytic agent

The novel anxiolytic drug buspirone raised striatal levels of the dopamine metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC) 1 hr after oral administration. This effect was dose-dependent with a peak at 60 min. No changes were observed in the levels of 3-methyxytyramine (3MT), the extraneuronal metabolite of dopamine. Noradrenaline, serotonin and its metabolite 5-hydroxyindoleacetic acid (5HIAA) were not affected. Buspirone displaced [³H]spiroperidol from striatal binding sites, with an ic₅₀ (1.8 × 10^?7 M), comparable to that of clozapine ($\text{ic}{}_{50}\text{= 1.4 × 10}{}^{\mathrm{?7}}\text{M}$) but considerably lower than that of haloperidol (4.7 × 10^?9 M). Buspirone was only a weak inhibitor of dopamine-stimulated adenyl cyclase. Buspirone was not active on the binding of trifluoperazine to calmodulin and did not modify calmodulin-induced activation of phosphodiesterase (PDE). Repeated administration of buspirone did not increase the number of DA receptors. These data show that, although buspirone has antidopaminergic activity, it can hardly be classified as a classic neuroleptic agent.     

Characterization of rat skeletal muscle monoamine oxidase.

Optimal conditions for deamination of 5-hydroxytryptamine in rat skeletal muscle were determined. The presence of monoamine oxidase (MAO) A and MAO B isozymes was demonstrated by the use of tyramine (a substrate of both forms), specific substrates (serotonin and benzylamine), and specific inhibitors (clorgyline and deprenyl) of MAO A and B respectively. A 6.5:3.5 ratio of MAO A to B was found using a whole muscle homogenate, while a 7.5:2.5 ratio was found with isolated mitochondria. Thermal inactivation studies demonstrated that skeletal muscle MAO A is more susceptible to heat inactivation than MAO B. The approximate proportion of muscle homogenate MAO which is present in sympathetic nerves was found to be 18 per cent, as determined by treating rats with 6-hydroxydopamine and quantifying the decrease in activity. Significant inhibition of MAO activity was observed after administration in vivo of the MAO inhibitors pargyline, tranylcypromine and harmaline.     

Inhibition patterns of monoamine oxidase in sub-fractions of rat brain mitochondria in presence of some selective inhibitors.

In vitro inhibition patterns of MAO activity in different mitochondrial sub-fractions of rat brain in presence of harmine, harmaline and deprenyl with tyramine and serotonin as substrates were investigated. The results indicate that type A and type B MAO are distributed in different ratios among the mitochondrial sub-fractions.     

Dansylarginine N-(3-ethyl-1,5-pentanediyl)amide: A potent and selective fluorescent inhibitor of butyrylcholinesterase

Interactions between dansylarginine N-(3-ethyl-1,5-pentanediyl)amide (DAPA) and the cholinesterases were examined by the techniques of enzyme kinetics and fluorescence spectroscopy. When tested with partially purified enzyme preparations, DAPA was a potent inhibitor of butyrylcholinesterase $\text{(}\text{IC}{}_{50}\text{= 2 × 10}{}^{\mathrm{?7}}\text{M}\text{)}$ but not of acetylcholinesterase $\text{(}\text{IC}{}_{50}\text{= 4 × 10}{}^{\mathrm{?4}}\text{M}\text{)}$. For a detailed study of the effects of DAPA on butyrylcholinesterase (BuChE), the enzyme was purified to homogeneity from horse serum, with the aid of affinity chromatography on N-methyl acridinium. The kinetics of the inhibition of purified BuChE by DAPA were complex, having both competitive and non-competitive features, and it was not possible to estimate K_i unambiguously. Spectroscopic measurements showed that the fluorescence of the dansyl moiety was strongly affected by the binding to BuChE. With excitation at 330 nm, total fluorescence emission from bound DAPA (at 450 nm and above) was 21-fold greater than from free DAPA. In a titration experiment, this enhancement of fluorescence intensity was used to calculate that each monomer of BuChE has two apparently independent DAPA-binding sites with a K_d of 4.5 × 10^?7 M. Further measurements showed that the fluorescence emission of bound DAPA was markedly blue-shifted (to 502 nm from 570 nm in free solution) and that the fluorescence lifetime of this form was greatly prolonged (to 24 nsec from 2.7 nsec). These observations indicate that the high affinity binding sites on BuChE lock DAPA in a highly non-polar environment.     

In vivo monoamine oxidase inhibition by d-amphetamine

In vitro, d- and l-amphetamine (AMPH) are reversible monoamine oxidase (MAO) type A inhibitors, the d-form being approximately five times more potent. Experiments were conducted in rats to determine whether MAO inhibition occurs in vivo. d-AMPH was more effective than l-AMPH at decreasing striatal 3,4-dihydroxyphenylacetic acid (DOPAC). However, assays of striatal MAO activity following administration of AMPH in vivo failed to show MAO inhibition. In other experiments, rats were treated with d-AMPH (zero time) followed by phcnelzine (1 hr), an irreversible MAO inhibitor, and were killed at 25 hr. MAO activity was determined in vitro for the striatum and the rest of the brain using serotonin (MAO-A) and phenylethylaminc (MAO-B) as substrates. d-AMPH provided significant protection against MAO-A inhibition by phenelzine, whereas l-AMPH and cocaine (used instead of AMPH) were without effect. d-AMPH failed to protect against MAO-B inhibition by phenelzine. Thus, d-AMPH appears to inhibit reversibly MAO type A in vivo. However, using the same ‘protection protocol’, d-AMPH failed to oppose phenelzine-induced lowering of striatal DOPAC. Experiments were undertaken to determine whether the protective effect of d-AMPH on MAO type A would influence striatal dopamine depletion by RO4-1284, a rapidly acting reserpine-like agent. RO4-1284-induced depletion of dopamine was inhibited by phenelzine. Prior treatment with d-AMPH reduced significantly the protective effect of phenelzine, suggesting reversible, intraneuronal MAO inhibition by d-AMPH in vivo. The possible neuronal mechanisms for these events are discussed.     

Turnover and synthesis of diamine oxidase (DAO) in rat tissues. Studies with heparin and cycloheximide

High diamine oxidase (DAO) and histamine activity are present in rat intestine, thymus and adrenals, and a close correlation exists between the two activities in these tissues (Biochem. Pharmac.24, 979 (1975)). The distribution of histaminase in normal and germ-free rat tissues and the release of this enzyme from intestine, thymus and adrenals was investigated in further detail with a tritium-release assay. Contrary to previous reports, histaminase activity was detected in brian, in the hypothalamus, thalamus and medulla but not in cortex and cerebellum. The enzyme was released by heparin into blood from intestine and adrenals but not from thymus. In high doses, heparin produced almost complete (>80 per cent) depletion of the enzyme in intestine within 1 hr. The enzyme activity reappeared and returned to normal levels by 24 hr. Prior administration of cycloheximide prevented the repletion of enzyme activity. The time course of the responses to the drugs suggested that DAO is synthesized continuously at a relatively rapid rate ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{～ 10}\text{hr}$). Studies in vitro indicated that DAO unlike monoamine oxidase diffuses from the mucosal surface into the lumen of the gut. DAO may therefore have a role in deaminating diamines of bacterial origin in the intestinal contents.     

Histamine release by fire ant (Solenopsis) venom.

Venoms from the fire ants Solenopsis invicta and S. geminata were free of detectable histamine but caused histamine release from rat peritoneal mast cells in vitro. On a per ant basis, venom from S. invicta ($\text{ed}{}_{50}\text{= 0·12}\text{venom reservoirs/ml}$) was four times as potent as venom from S. geminata ($\text{ed}{}_{50}\text{= 0·54}\text{venom reservoirs/ml}$). Hexane extracts of venom and a synthetic piperidine were as effective as the venom itself in producing histamine release, indicating that the piperidines in the venom are responsible for most of the activity. Intradermal injection of venom from S. geminata into human subjects produced dose-dependent wheals and subjective responses (itch and/or pain). Ten nanograms of histamine produced effects approximately equivalent to the venom of a single ant and the antihistamine diphenhydramine significantly reduced the wheal and subjective responses to the venom. It was concluded that histamine release plays a major role in the action of fire ant venoms.     

Rate-determining factors for ethanol metabolism in fasted and castrated male rats

The effects of castration and fasting upon the alcohol elimination rate, liver alcohol dehydrogenase (LADH) maximum activity (V_max), and hepatic concentrations of ethanol, acetaldehyde, and free NADH during ethanol oxidation were examined in male Wistar rats. Castration increased the V_max of LADH and, to a lesser extent, the alcohol elimination rate in vivo. On the other hand, fasting reduced the V_max of LADH and the alcohol elimination rate in sham-operated and castrated rats but it did not nullify the effect of castration. Castration produced small but significant changes in the hepatic concentrations of ethanol, acetyldehyde and free NADH in fed rats during ethanol oxidation. Fasting also caused significant increases in the concentration of free NADH during alcohol oxidation in both the sham-operated and castrated groups. The ratio of the steady-state velocities of LADH in situ to the maximum velocities of LADH ($\text{ν}\text{V}{}_{\mathrm{<mtext>max</mtext>}}$) under the different experimental conditions was calculated by using the steady-state rate equation for the enzyme mechanism of rat LADH and its kinetic constants. The calculated $\text{ν}\text{V}{}_{\mathrm{<mtext>max</mtext>}}$ ratios were 50–62%, indicating that LADH activity was limited to about the same extent by its substrates and products under these conditions and that the changes in alcohol elimination rates produced by fasting and castration mainly reflected changes in the V_max of LADH. The calculated steady-state velocities in situ (ν) were 14–28% lower than the measured rates of alcohol elimination in vivo. The extent of agreement is probably acceptable in view of the assumptions needed to determine the free NADH concentration in liver and the existence of non-LADH-related processes for alcohol elimination in vivo.     

Mechanism of action of 5'-methylthioadenosine in S49 cells

5'-Deoxy-5'-methylthioadenosine, a naturally occurring co-product of polyamine biosyn-thesis, has been shown to inhibit a variety of biological processes. To investigate the mode of action of this nucleoside and to assess the involvement of cAMP in this action, the effect of methylthioadenosine on S49 wild type and two cAMP-related mutant cells was examined. The sulfur-containing nucleoside potently inhibited the growth of the parental strain ($\text{IC}{}_{50}\text{= 50 μ}\text{M}$), whereas nearly 10-fold greater resistance was demonstrated by S49 adenylate cyclase deficient ($\text{IC}{}_{50}\text{= 420 μ}\text{M}$) and S49 cAMP-dependent protein kinase deficient ($\text{IC}{}_{50}\text{= 520 μ}\text{M}$) mutant cells. Methylthioadenosine was shown to competitively inhibit the S49-derived high-affinity cAMP phosphodiesterase (K_i = 62 μM) in vitro, whereas methylthioadenosine phosphorylase activity was equivalent in all three cell types. The intracellular levels of the regulatory nucleotide, cAMP, increased dramatically in the wild type (17-fold) and protein kinase deficient (6-fold) strains in response to 100 μM concentrations of the drug. It is concluded that the growth arrest produced by 5'-methylthioadenosine in S49 cells is primarily due to the inhibition of cAMP phosphodiesterase and the subsequent increase in cAMP levels that result.     

Determination of extraction constant,true partition coefficient and formation constant of ion-pair complexes of quaternary ammonium salts,tetrabutylammonium bromide and isopropamide iodide.with some organic anions by a solvent extraction technique

A new method of determining the extraction constant (K_e, the true partition coefficient (TPC) and the formation constant (K_f) of ion-pairs, was developed by the solvent extraction technique. K_e and TPC were estimated from the reciprocals of the intercept and the slope of the regression line obtained by plotting

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{vs}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}$

in the following equation.

$\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{APC ? dA}\text{=}\text{1}\text{K}{}_{\mathrm{e}}\text{+}\text{B}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{dA}\text{APC ? dA}\text{+}\text{A}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{+}\text{B}{}^{\mathrm{T}}{}_{\mathrm{W}}\text{x}\text{1}\text{TPC}$

where [A^T_W] and [B^T_W] are the total concentrations of the cationic compound A and that of the anionic compound B in the aqueous phase respectively, APC is the apparent partition coefficient of A, dA is the partition coefficient of cation A⁺. K_f, which is expressed by K_e/TPC, was then calculated. These constants were determined for the ion-pair extraction of tetrabutylammonium bromide and isopropamide iodide with 4 organic anions, i.e. benzoic acid, p-toluenesulfonic acid, salicylic acid and taurodeoxycholic acid. This new method might be applicable to other ion-pairs without further assumptions except that the molar ratio of the ion-pair formation be 1 : 1.     

Comparison of the activity of 2'-deoxycoformycin and erythro-9-(2-hydroxy-3-nonyl)adenine in vivo.

The inhibition of P388 cell deamination of arabinosyladenine (ara-A) in vivo by the adenosine deaminase inhibitors 2′-deoxycoformycin (dCF) and erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and their subsequent effects on ara-A metabolism were determined and compared. A single i.p. injection of EHNA (3 mg/kg, 10.9 μmoles/kg) initially inhibited ara-A deamination in vivo by 96 per cent with recovery to 50 per cent of control values within 30 min. In comparison, dCF (0.2 mg/kg, 0.75 μmole/kg) inhibition of ara-A deamination was initially low (4 per cent), but maximized (96 per cent) after 15 min. This inhibition was sustained for 2 hr and did not recover to 50 per cent of control values until after 10 hr. Injected alone, the $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of ara-A in the peritoneal ascitic fluid was less than 1 min, but was increased to 7 min when injected with EHNA and to 12 min when injected 15 min after dCF. The rate of efflux of ara-A and its metabolites from the peritoneal cavity ($\text{T}{}_{\mathrm{<mtext>case1</mtext><mtext>2</mtext>}}\text{= 15?18}\text{min}$) was not affected significantly by either deaminase inhibitor. Cellulat ara-ATP concentrations were elevated and the extent and duration of inhibition of DNA synthetic capacity were increased identically in cells of mice treated with ara-A and either deaminase inhibitor as compared with those treated with ara-A alone. Sustained deaminase inhibition after intraperitoneal concentrations of ara-A had been diminished by otherwise normal disposition did not augment the biochemically demonstrable activity of ara-A. Therefore, it appears that maintenance of the initial high concentrations of ara-A is the primary function of a deaminase inhibitor in increasing the therapeutic efficacy of this analog.     

Isolation and characterization of the main toxic fraction from the venom of the false horned viper (Pseudocerastes fieldi)

R. Batzri-Izraeli and A. Bdolah. Isolation and characterization of the main toxic fraction from the venom of the false horned viper (Pseudocerastes fieldi). Toxicon20, 867–875, 1982—The venom of Pseudocerastes fieldi was subjected to gel filtration on Sephadex G-75. Most of the protein and lethality of the venom were eluted in a major symmetrical peak (C). The lethality of this peak is confined to a basic protein fraction, Cb (pI > 9.5) separable by DEAE-cellulose chromatography. Two proteins with molecular sizes close to 16,000 daltons were isolated from this fraction by preparative acidic gel electrophoresis in the presence of Triton X-100. One of the proteins (CbII) is lethal to mice ($\text{ld}{}_{50}\text{= 1}\text{mg/kg}$) and shows phospholipase A activity as well as direct hemolytic activity. The other protein (CbI) does not reveal any known biological activity. However, upon recombination of the two a synergistic lethal activity is evident ($\text{the}\text{ld}{}_{50}\text{of the mixture = 0.25 mg/kg}$). It is suggested that CbI may be a specifier which potentiates the toxicity of the phospholipase A at the target site.     

The monoamine oxidase inhibitors clorgyline and L-deprenyl also affect the uptake of dopamine, noradrenaline and serotonin by rat brain synaptosomal preparations

Clorgyline and l-deprenyl are, respectively, specific type A and type B monoamine oxidase (MAO) inhibitors. We investigated the effects of these two drugs as differential inhibitors of synaptosomal amine uptake and determined how far these effects might be predicted from their properties as specific MAO-A and MAO-B inhibitors. The rank order of inhibition of uptake by clorgyline was found to be: serotonin (ic₅₀ = 10 μM) dopamine (ic₅₀ = 56 μM) noradrenaline (ic₅₀ = 66 μM). The rank order of inhibition of uptake by l-deprenyl was: noradrenaline (ic₅₀ = 26 μM) serotonin (ic₅₀ = 460 μM) dopamine (ic₅₀ = 530 μM). The observation that clorgyline is a more specific inhibitor of the uptake of serotonin (a type A MAO substrate) is consistent with its activity as a type A MAO inhibitor. Paradoxically, L-deprenyl, though a type B MAO inhibitor, is fairly effective at inhibiting the uptake of noradrenaline (a type A MAO substrate).