Tachykinins Influence Interdigestive Rhythm and Contractile Strength of Human Small Intestine

The effect of the putative entericneurotransmitters neurokinin A and substance P wereinvestigated on human small intestinal motility. Eitherneurokinin A, at doses of 6-25 pmol/kg/min, or substanceP at doses of 1- 6 pmol/kg/min were administeredintravenously to healthy volunteers over 4 hr.Neurokinin A dose-dependently increased the fraction ofphase II of the migrating motor complex, contraction frequency, motility index, and amplitude ofcontractions. At the highest dose, neurokinin A induceda phase II-like pattern, disrupting the migratingmyoelectric complex. Substance P dose-dependentlyincreased phase II of the migrating motor complex. Thecontraction frequency increased slightly at the highestdose, but neither motility index nor contractionamplitude changed. It is concluded that neurokinin A and substance P stimulate small intestinalmotility in man, and it can be speculated that they playa role in the control of human small intestinalmotility.     

Epitope-specific TCRbeta repertoire diversity imparts no functional advantage on the CD8+ T cell response to cognate viral peptides

TCR repertoire diversity has been convincingly shown to facilitate responsiveness of CD8+ T cell populations to mutant virus peptides, thereby safeguarding against viral escape. However, the impact of repertoire diversity on the functionality of the CD8+ T cell response to cognate peptide-MHC class I complex (pMHC) recognition remains unclear. Here, we have compared TCRbeta chain repertoires of three influenza A epitope-specific CD8+ T cell responses in C57BL/6 (B6) mice: D(b)NP(366-374), D(b)PA(224-233), and a recently described epitope derived from the +1 reading frame of the influenza viral polymerase B subunit (residues 62-70) (D(b)PB1-F2(62)). Corresponding to the relative antigenicity of the respective pMHCs, and irrespective of the location of prominent residues, the D(b)PA(224)- and D(b)PB1-F2(62)-specific repertoires were similarly diverse, whereas the D(b)NP(366) population was substantially narrower. Importantly, parallel analysis of response magnitude, cytotoxicity, TCR avidity, and cytokine production for the three epitope-specific responses revealed no obvious functional advantage conferred by increased T cell repertoire diversity. Thus, whereas a diverse repertoire may be important for recognition of epitope variants, its effect on the response to cognate pMHC recognition appears minimal.     

Acute Sporadic Non-A Non-B Hepatitis in an Urban Community in New Zealand

Abstract: Acute sporadic non-A non-B hepatitis in an urban community in New Zealand. P. N. Goldwater, D. G. Woodfield, R. A. Anderson, M. B. Gill and S. Carpenter, Aust. N.Z. J. Med. , 1982, 12, pp. 268–271.
Acute sporadic non-A, non-B hepatitis is reported for the first time in New Zealand. Examination of sera from 94 patients with biochemical evidence of hepatitis showed that 26 (27%) had acute hepatitis B (HB), 22 (23%) had acute hepatitis A (HA) and 25 (26%) had acute non-A, non-B hepatitis (NANBH). Nine (10%) patients had Epstein-Barr virus (EBV) associated hepatitis and one (1%) had cytomegalovirus (CMV) hepatitis. There were 11 (13%) patients with mixed infections; eight with HA plus HB, one with HB plus EBV, one with HA plus EBV and one with HB plus CMV.
Thus NANBH and EBV associated hepatitis must be considered in the differential diagnosis of patients presenting with clinical hepatitis with no history of possible percutaneous infection.     

Occurrence of respiratory syncytial virus subtypes in hospitalized children in Cleveland, Ohio from 1985 to 1988.

In order to determine the frequency of occurrence of the two respiratory syncytial virus (RSV) subtypes in hospitalized children in Cleveland, Ohio, we analyzed clinical isolates obtained during three consecutive winter epidemic seasons between 1985 and 1988. RSV was recovered from the frozen clinical specimens of 197 patients: 176 subtype A, and 21 subtype B. Subtype A predominated during all three epidemic seasons, ranging from 83 to 94% of isolates. We surveyed the clinical records of 16 children with subtype B, and 101 children with subtype A infections, hospitalized at the University Hospitals of Cleveland during these winter epidemics and found no differences in age, sex, race, or clinical spectrum of severity of disease caused by the two subtypes. In contrast to previously reported data, subtype A predominated in each of the winter seasons studied within this community. We conclude that both subtypes circulate concurrently within the community during the winter. In hospitalized children both subtypes appear to cause a similar spectrum of disease. Both the concurrent circulation of RSV subtypes and the similar spectrum of illness pose for important considerations in the development of effective vaccines against this common respiratory agent in children.     

Structure of NDP-forming Acetyl-CoA synthetase ACD1 reveals a large rearrangement for phosphoryl transfer

The NDP-forming acyl-CoA synthetases (ACDs) catalyze the conversion of various CoA thioesters to the corresponding acids, conserving their chemical energy in form of ATP. The ACDs are the major energy-conserving enzymes in sugar and peptide fermentation of hyperthermophilic archaea. They are considered to be primordial enzymes of ATP synthesis in the early evolution of life. We present the first crystal structures, to our knowledge, of an ACD from the hyperthermophilic archaeon Candidatus Korachaeum cryptofilum. These structures reveal a unique arrangement of the ACD subunits alpha and beta within an α₂β₂-heterotetrameric complex. This arrangement significantly differs from other members of the superfamily. To transmit an activated phosphoryl moiety from the Ac-CoA binding site (within the alpha subunit) to the NDP-binding site (within the beta subunit), a distance of 51 Å has to be bridged. This transmission requires a larger rearrangement within the protein complex involving a 21-aa-long phosphohistidine-containing segment of the alpha subunit. Spatial restraints of the interaction of this segment with the beta subunit explain the necessity for a second highly conserved His residue within the beta subunit. The data support the proposed four-step reaction mechanism of ACDs, coupling acyl-CoA thioesters with ATP synthesis. Furthermore, the determined crystal structure of the complex with bound Ac-CoA allows first insight, to our knowledge, into the determinants for acyl-CoA substrate specificity. The composition and size of loops protruding into the binding pocket of acyl-CoA are determined by the individual arrangement of the characteristic subdomains.NDP-forming acyl-CoA synthetases (ACDs) catalyze the conversion of acyl-CoA thioesters to the corresponding acids and couple this reaction with the synthesis of ATP via the mechanism of substrate-level phosphorylation. ACDs have been studied in detail in hyperthermophilic archaea, where they function as the major energy-conserving enzymes in the course of anaerobic sugar and peptide fermentation (1–4). It is believed that ACDs represent a primordial mechanism of ATP synthesis in the early evolution of life. ACDs were found in all acetate (acid)-forming archaea (5, 6) and in the eukaryotic parasitic protists Entamoeba histolytica (7) and Giardia lamblia (8), but they have not been found in acetate-forming bacteria. In bacteria, with the exception of Chloroflexus (9), the conversion of inorganic phosphate and the thioester acetyl (Ac)-CoA to acetate and ATP is catalyzed by two enzymes, phosphate Ac-transferase and acetate kinase (10). Following the identification of ACD genes (5, 11) a novel protein superfamily of NDP-forming ACDs was proposed by a bioinformatics analysis (8). In addition to ACDs, this superfamily contains the well-characterized succinyl-CoA synthetases (SCSs) and ATP-citrate lyases (ACLYs) (8). Each ACD is composed of at least five subdomains with variable sequential arrangement (8). This phenomenon, termed “domain shuffling,” is one of the key features of this superfamily (8). Superposition of several structures of SCS from Escherichia coli (ecSCS) (12–14), Thermus aquaticus (15), the mammalian GTP-specific SCS from pig (16), and a truncated form of human ACLY (17, 18) revealed that subdomains 1–5 share a common arrangement in these enzymes. From detailed studies of the reaction mechanism of ecSCS, a crucial enzyme tightly connected to the TCA cycle, a three-step mechanism was proposed, which involves the phosphorylation of a highly conserved His residue at the first active site (site I) as an intermediate step (12, 13). Subsequently, the phosphoryl moiety is transferred onto an NDP that is bound at the second active site (site II). The distance of around 36 Å between site I and site II is assumed to be bridged by a so-called “swinging loop” (12, 14, 19). A mechanism comparable to the mechanism of the SCSs was presumed for the ACDs (20). A study based on sequence, biochemical, and mutational analyses identified a highly conserved and functional relevant His residue within the beta subunit of the ACDs (20). Of note, the SCS enzymes do not contain a comparable His residue. Thus, an extension of the mechanism by a fourth step was suggested for the ACD1 from Pyrococcus furiosus (20). Here, the second His residue is thought to serve as an additional intermediate, which gets phosphorylated transiently during the enzymatic reaction and subsequently transmits the phosphoryl moiety onto the bound NDP. The necessity for a four-step mechanism may originate from a shortening of the proposed swinging loop, which facilitates the phosphoryl transfer between the subunits (20). However, due to the completely different arrangement of the subdomains within ACD [alpha(1-2-5)/beta(3-4)] in comparison to ecSCS [alpha(1-2)/beta(3-4-5)], a different 3D arrangement of the subdomains in ACD and, as a consequence, a variation of the proposed reaction steps has to be considered.ACDs are versatile enzymes that are capable of metabolizing a variety of CoA thioesters generated in the course of sugar and peptide fermentation (3, 4, 21). In contrast, the ecSCS specifically binds succinyl-CoA, accepting only small aliphatic CoA thioesters as additional substrates (22). The ACLY is even more specific for Ac-CoA (23). Because ACDs are involved in sugar and amino acid metabolism, they are ambivalent regarding their converted substrates (3, 4, 24, 25). In addition, domain shuffling creates a very diverse pattern of subdomain organization within members of the ACD family (8). Some ACD enzymes are even built up as single-chain proteins with fused alpha-beta or beta-alpha subunits. The linker region between the fused subunits is usually very short (8). Therefore, a structural model for ACDs based on the structure of ecSCS as presented by Bräsen et al. (20) cannot be fully compatible with those single-chain ACDs, because distances of more than 60 Å between the termini of individual alpha and beta subunits must be bridged.So far, there are no structural data to explain these described peculiarities (necessity of a second His, different arrangement of the subdomains, and broader substrate selectivity). In this study, we present a comprehensive analysis of various crystal structures of the functional complex of the ACD isoform 1 from the hyperthermophilic archaeon Candidatus Korarchaeum cryptofilum (ckcACD1). Ca. K. cryptofilum belongs to the most ancestral archaea (26). Based on genome analyses, Ca. K. cryptofilum has been proposed to ferment amino acids using ACDs as major energy-conserving enzymes (26). Three ACD isoenzymes with different substrate specificities have been characterized (27). ckcACD1 converts small aliphatic CoA thioesters. It is composed of four protein chains (two alpha subunits and two beta subunits) that form an α₂β₂-heterotetramer. Each alpha subunit has one active site for acyl-CoA binding, and each beta subunit has one active site for NDP binding. Due to its similar molecular composition and kinetic properties as ACD1 from the hyperthermophilic archaeon P. furiosus (pfACD1), it is likely that ckcACD1 follows the same four-step catalytic reaction mechanism as has been proposed for the homologous pfACD1 (20). In particular, the structural rearrangements accompanying the phosphate shuttle process between alpha and beta subunits of ACD will be described for the first time to our knowledge. This work provides direct evidence for the proposed loop swinging, which, in addition, can explain the necessity for a second active-site His located in the beta subunit near site II. Further detailed analysis of the binding mode of Ac-CoA to ckcACD1 provides insight into substrate specificity of the enzyme.     

Muscle protein catabolism in diabetes: 3-Methylhistidine excretion in the spontaneously diabetic “BB” rat

The muscle protein lost in uncontrolled diabetes may be due to decreased synthesis, increased catabolism, or to any combination of alteration in these rates that results in net loss. Differing methods of examining these rates in vivo and in vitro have given conflicting results. We assessed the rate of catabolism of proteins containing 3-methylhistidine (3-MH) by measurement of its urinary excretion in spontaneously diabetic “BB” Wistar rats. Prior to overt diabetes, rates of excretion were appropriate to the age of the rats (1.46 ± 0.15 μmole/day), with 34%–47% as the nonacetylated form. Accompanying diabetes there was an increase in urine urea nitrogen of two to threefold over 4–14 days, and an increase in ammonium nitrogen of sixfold. 3-MH excretion doubled by 4 days, and 81%–96% was excreted as the nonacetylated form. Subcutaneous insulin in doses sufficient to improve glycosuria and hyperglycemia was associated with normalized total 3-MH excretion (N-acetyl 3-MH plus 3-MH) but a greater proportion than normal appeared in the nonacetylated form. These results suggest that muscle protein catabolism increased with insulin deficiency and that this defect can be corrected by therapy. Both untreated and treated diabetic rats appear to have a limited capacity for acetylation of 3-MH prior to its excretion.     

Effect of isosorbide dinitrate on response to submaximal and maximal exercise in patients with congestive heart failure.

Isosorbide dinitrate is an effective vasodilator that improves resting left ventricular performance in patients with congestive heart failure, but little is known of the effect of the drug on the response to exercise. Bicycle exercise to symptomatic maximum was performed by 18 patients with class II to IV congestive heart failure before and 90 minutes after administration of isosorbide dinitrate, 40 mg orally. Although resting pulmonary wedge pressure and systemic vascular resistance were significantly reduced after isosorbide dinitrate, exercise duration was not altered and maximal oxygen consumption was not significantly changed (13.6 +/- 1.3 [SEM] standard error of the mean versus 13.8 +/- 1.2 ml/kg per min). At peak exercise pulmonary wedge pressure of 37.1 +/- 1.7 mm Hg, cardiac index of 4.19 +/- 0.35 liters/min per m2, and systemic vascular resistance of 14.7 +/- 1.3 units were not significantly different after nitrate administration. However, at submaximal loads, pulmonary wedge pressure was reduced from 33.6 +/- 1.7 to 27.9 +/- 1.8 mm Hg (P less than 0.01), and systemic resistance from 16.5 +/- 1.5 to 13.7 +/- 1.0 units (P less than 0.01) after administration of isosorbide dinitrate. Thus, short-term administration of nitrates does not improve maximal exercise capacity or left ventricular performance at maximal exercise in patients with congestive heart failure, but it does appear to improve pump function at submaximal work loads and may therefore enable patients to perform limited exercise more comfortably.