Photolysis and ozonolysis of (iso) desmosine-containing crosslinked peptides from porcine aorta elastin

This report describes the use of photolysis and ozonolysis as a means of achieving complete cleavage of the pyridinium ring of (iso)desmosine in crosslinked elastin peptides. Although photolysis leads to the opening of the ring with concomitant formation of lysine, the peptide chains remain attached. Subsequent ozonolysis is able to completely achieve the cleavage of the rest of the ring skeleton, thus leading to the separation of the peptide chains. Formation of new amino acids, i.e. α-aminoadipic and glutamic acids, is emphasized. Localization of these amino acids within the released peptides should be of help in structural investigations on the crosslinking zones involving either isodesmosine or desmosine. However, other amino acids such as tyrosine and phenylalanine are sensitive to this procedure and side reactions occur which are responsible for peptide bond cleavage with the formation of breakdown products.     

Er:YAG激光乳化晶体术对猪眼前房及切口部组织温度的影响

目的观察激光乳化晶体过程中眼部组织的温度变化.方法使用针式传感器数字型温度计,测量ErYAG激光乳化晶体过程中离体猪眼球前房、角膜深层及角膜缘切口三部位组织温度.结果前房灌注条件下行激光乳化时,各部位组织温度升高幅度均在1.0℃以下;而在非灌注条件下激光乳化时前房温度升高幅度最大,为14.6℃,实测温度36.1±0.63℃,且均为前房温度＞角膜深层＞角膜缘切口(p＜0.01);同一部位、同一时刻3种激光能量的平均温度,前房非灌注条件下激光乳化温度升高幅度＞前房灌注条件下激光乳化(p＜0.01).结论前房灌注条件下行ErYAG激光乳化晶体过程中,前房、角膜深层及切口周围的组织温度升高幅度明显低于前房未灌注条件下的激光乳化;在前房非灌注条件下,ErYAG激光乳化晶体可使前房、角膜深层及角膜缘切口周围组织温度明显升高,升高幅度与激光能量成正比,前房温度升高幅度最大.     

Characteristics of the Photoconversion of Rhodopsin in the Early Stages of Photolysis

Low-temperature spectrophotometry was used to study the primary stages of rhodopsin photolysis. A digitonin extract of rhodopsin was irradiated at -155 degrees C with blue light of wavelength 436 nm. The stage of the bathorhodopsin --> lumirhodopsin conversion was accompanied by the simultaneous formation of several products. Formation of an intermediate product spectrally similar to the known "blue-shifted intermediate" (BSI) was demonstrated. It is suggested that the appearance of more than one intermediate product at each stage of photolysis reflects the existence of several conformational states of the rhodopsin molecule during its photoconversion.     

The kinetics of intermediate processes in the photolysis of bovine rhodopsin--II. The intermediate decay sequence from lumirhodopsin497 to metarhodopsin380 II.

The kinetics of early intermediate processes in the thermal decay sequence following illumination of the bovine visual pigment, rhodopsin, have been studied using flash photolysis. It is found that the conversion of lumirhodopsin₄₉₇ to metarhodopsin₄₈₀ I in rod disc suspensions above 0°C can best be interpreted as a second-order process exhibiting pseudo first-order behavior in its terminal stages. The subsequent conversion of metarhodopsin₄₈₀ I to metarhodopsin₃₈₀ II is a single first-order process in rod disc suspensions.At low temperatures (from ?40 to ?50°C) the lumirhodopsin₄₉₇→ metarhodopsin₄₈₀ I reaction is characterized by relatively large, positive values ofΔH^≠ and ΔS^≠, white at higher temperatures, above 3°C, this same process has a very small ΔH^≠ and slightly negative ΔS^≠. In addition the ratios of initial concentrations of the reactants varies by a factor of ~10 in the two temperature ranges studied. The subsequent metarhodopsin ₄₈₀ I → metarhodopsin ₃₈₀ II reaction most likely involves rather marked protein configurational changes as indicated by the large, positive values of ΔH^≠ and ΔS^≠ for this first-order process.     

Photoactivation of intracellular guanosine triphosphate analogues reduces the amplitude and slows the kinetics of voltage-activated calcium channel currents in sensory neurones

The influence of guanine nucleotide analogues on calcium channel currents in cultured rat dorsal root ganglion neurones has been studied using a technique in which the rate of diffusion of the analogues to their site of action is by-passed by photochemical release of the analogues within the neurones. The 1(2-nitrophenyl)ethyl P³-ester derivatives of guanosine 5-0(3-thio)triphosphate (caged GTP--S) and 5-guanylylimidodiphosphate (caged GMP-PNP) were synthesised and found to be completely photolysable by light, yielding free GTP--S and GMP-PNP. Calcium channel currents were recorded using the whole cell patch technique and either caged GTP--S or caged GMP-PNP (2 mM) were included in the patch pipette. Stable currents were recorded for 5–10 min, and a single pulse of 300–350 nm irradiation was directed using a liquid light guide onto the recording dish. Calcium channel currents were then recorded every 30–120 s following photochemical release of approximately 20M GTP-gg-S. The peak calcium channel current was reduced by about 70% with a slow time course [t _1/2 1.5±0.2 min (mean±SEM);n=5]. The transient component of the peak current was usually completely abolished, whereas the sustained current measured at the end of the 100 ms depolarising pulse was less affected. Qualitatively similar effects were observed on photolysis of caged GMP-PNP. These results suggest that the channels underlying the transient and the sustained components of the whole cell current may be differentially molulated by GTP analogues.     

N-甲氧基偕卤代亚胺化学性质的研究

N-甲氧基偕卤代亚胺经锌还原或光解都以高产率获得相应的腈,进一步探索该化合物的其它化学性质以适用于更复杂的情况。     

UVB photolysis of hydrocortisone 21-acetate

Hydrocortisone 21-acetate (HCA) in methanol solution undergoes photodegradation under UVB light, as monitored by HPLC. Five main photoproducts have been isolated and characterized by means of NMR and mass spectroscopy. One of them derives from a Norrish I photoreaction which cleaves the C17-C20 bond of the steroid yielding the andro-derivative, a second product comes from a Yang-type photorearrangement which links C18 to C20 yielding a cyclobutane adduct. The former photoproduct, in turn, undergoes further photolysis giving rise to various photoproducts, of which three have been characterized. The first is a stereoisomer of the andro-derivative, the others arise from the opening of the five-membered ring. HCA also proved photounstable in the solid state and in a commercial formulation for topical use, thus confirming the requirements of the Pharmacopeias for light protection of this drug. Indeed, experiments on LPS-stimulated THP-1 cells demonstrated the loss of anti-inflammatory activity when HCA was UVB-photodegraded. The radical mechanism involved in HCA photolysis seems also responsible for the in vitro photohemolytic effect and lipid peroxidation induced by HCA in combination with UVB light.     

Primary intermediates of rhodopsin studied by low temperature spectrophotometry and laser photolysis. Bathorhodopsin, hypsorhodopsin and photorhodopsin

The primary photochemical processes of rhodopsin studied by low temperature spectrophotometry and picosecond laser spectroscopy in our group was summarized. Low temperature spectroscopic experiments demonstrated that the retinylidene chromophores of hypso- and bathorhodopsins are in a twisted all-trans forms. Excitation of rhodopsin with 532 nm laser pulse (width: 25 psec) yielded a new bathochromic photoproduct "photorhodopsin"; its spectrum was located at longer wavelengths than that of bathorhodopsin. Photorhodopsin decays to bathorhodopsin with time constants of about 200 psec in squid and 40 psec in cattle. Squid and octopus hypsorhodopsins were produced within 25 psec by high energy pulse, but not by low energy pulse. Thus hypsorhodopsin is produced by two photon reactions (sequential two photochemical reactions) and decayed to bathorhodopsin with time constant of 125 psec.     

Layer selective presynaptic modulation of excitatory inputs to hippocampal cornu Ammon 1 by mu-opioid receptor activation

Chronic and acute activation of mu-opioid receptors (MOR) in hippocampal cornu Ammon 1 (CA1) disrupts rhythmic activity, alters activity-dependent synaptic plasticity and impairs spatial memory formation. In CA1, MORs act by hyperpolarizing inhibitory interneurons and suppressing inhibitory synaptic transmission. MOR modulation of inhibitory synaptic function translates into an increase in excitatory activity in all layers of CA1. However, the exact anatomical sites for MOR actions are not completely known. Therefore, we used voltage-sensitive dye imaging, whole cell patch clamping, photolysis of alpha-carboxy-2-nitrobenzyl ester, trifluoroacetic acid salt (CNB) -caged GABA, and micro-sectioned slices of rat hippocampus to investigate the effect of MOR activation in CA1. First, we investigated the effect of MOR activation using a MOR agonist [d-Ala2, NMe-Phe4, Gly-ol5]-enkephalin (DAMGO) on the direct activation of GABA receptors by photolysis of CNB-caged GABA in all layers of CA1. MOR activation did not affect hyperpolarizations due to direct GABA receptor activation in any layer of CA1, but MOR activation did suppress GABAergic inhibitory postsynaptic potentials suggesting that MOR activation acts by presynaptically inhibiting interneuron function. We next examined whether MOR activation was equivalently effective in all anatomical layers of CA1. To do this, cuts were made between anatomical layers of CA1 and isolated layers were stimulated electrically (five pulses at 20 Hz) to produce excitatory postsynaptic potentials (EPSPs). Under these conditions, MOR activation significantly increased EPSP areas in stratum radiatum (SR), stratum pyramidale (SP) and stratum oriens (SO) relative to stratum lacunosum-moleculare (SLM). When compared with the effect of GABA(A) and GABA(B) receptor antagonists on EPSP areas, the effect of DAMGO was proportionately larger in SR, SP and SO than in SLM. We conclude that MOR activation is more effective at directly modulating activity in SR, SP and SO, and the smaller effect in SLM is likely due to a smaller MOR inhibition of GABA release in SLM.     

Level of Flt3-ligand in plasma: a possible new bio-indicator for radiation-induced aplasia

Purpose : To follow plasma Flt3-ligand (FL) concentrations in irradiated animals in order to evaluate it as an indicator of bone marrow damage for the management of accidental radiation-induced aplasia. Materials and methods : Non-human primates were irradiated at doses ranging from 2 to 8 Gy, using whole- or partial-body irradiation. Plasma FL concentrations and blood cell counts were determined daily. Results : FL concentrations increased as early as day 2 after irradiation, whatever the irradiation dose. Increase in plasma FL concentration on day 5 post-irradiation was correlated with radiation dose and with the severity of radiation-induced aplasia. During the course of aplasia, FL concentrations in plasma were inversely correlated with neutrophil counts. A peak in FL concentration appeared before the neutrophil nadir, and the subsequent decrease in FL concentration was correlated with the recovery of blood-cell populations. Conclusions : Monitoring plasma FL concentration can be used as an indicator of radiation-induced marrow aplasia, and this may be of use in accidental irradiation situations.