Intraglottal pressure distribution computed from empirical velocity data in canine larynx

Intraglottal velocity measurements were taken using particle image velocimetry and the corresponding estimates for the intraglottal pressure were computed using the pressure Poisson equation. Results from five canine larynges showed that when the flow separated from the divergent glottal walls during closing, the vortices that were formed in the separated region of the glottis created negative pressure near the superior aspect of the folds. The magnitude of the negative pressure was directly proportional to the subglottal pressure. At low subglottal pressure, negative pressures at the superior edge were not observed when the divergence angle of the wall was minimal and the glottal flow did not separate from the wall.     

Distribution of the zot (zonula occludens toxin) gene among strains of Vibrio cholerae 01 and non-01

Abstract The distribution of the zot gene that encodes the zonula occludens toxin, a newly described toxin of Vibrio cholerae , among clinical, environmental and food isolates of V. cholerae 01 and non-01 was investigated. Both the zot gene and the ctx gene that encode cholera toxin were found in 247 of 257 clinical strains and 62 of 415 environmental or food isolates of V. cholerae 01. The zot gene, but not the ctx gene was found in 37 strains (one clinical strain and 36 environmental or food isolates). In addition, two of 31 clinical strains and six of 98 environmental or food isolates of V. cholerae non-01 possessed both the zot gene and the ctx gene. These results demonstrated the predominantly concurrent occurrence of the zot gene and ctx genes among strains of V. cholerae 01 which suggests a possible synergistic role of ZOT in the causation of acute dehydrating diarrhea produced by V. cholerae 01.     

Biological activity of des-(Asp1, Arg2, Val3)-angiotensin II in man

When des-(Asp¹, Arg², Val³)-angiotensin II was infused iv at rates of 308–5,550 pmol/kg·min for 10–120 min into 5 normal men and 2 patients with Bartter's syndrome, no significant change was observed in blood pressure (BP), plasma renin activity (PRA) or plasma aldosterone (PA), and the lowest dose did not inhibit a captopril-induced increase in PRA in the normal men, although des-(Asp¹, Arg²)-angiotensin II was reported in the same 5 normal men to cause a decrease in PRA and an increase in PA in this dose range and a rise in BP at 2,220 and 5,550 pmol/kg·min. However, an iv infusion of the pentapeptide at 9,000 pmol/kg·min for 15 min significantly raised BP in the 5 normal men but not in patients with Bartter's syndrome. BP returned to the pretreatment level 60 min after the cessation of the infusion, although the duration of the pressor actions of angiotensin II, angiotensin III and des-(Asp¹, Arg²)-angiotensin II were reported to be within 5 min in man. At the same dose level none of the 7 examined subjects showed any significant change in PRA or PA. Des-(Asp¹, Arg², Val³, Tyr⁴)-angiotensin II was infused iv at a rate of 41,480 pmol/kg·min into one of the normal men, but it caused no significant change in BP, PRA or PA. These results suggest that the pentapeptide and probably the tetrapeptide do not possess renin-suppressing and steroidogenic actions in man but the pentapeptide does elecit a minimal pressor action with a prolonged duration.     

Sport for tall.

Eight new events (handball, basketball, and six rowing events) were introduced for women in the Olympic Games at Montreal in 1976. Of 187 women rowers who competed at Montreal, none was shorter than the mean height (162 cm, 64 in) of women aged 18-24 in the United States. In team events only two out of 250 participants were shorter than the reference mean. Even among the tall, it was the taller participants who won medals. What does the slogan "Sport for All" mean in this context? Moreover, the physical size required of champion rowers and basketball players is not to be found in some Asian, African, and Latin American populations. International contests in many such events therefore seem to be at variance with the first charter of the Olympic Games. An independent reviewing body is urgently needed to examine the merits of man made rules in many sporting contests.     

Obesity and Smoking Habits

A large-scale survey of steel workers in South Wales has shown a considerable difference between the body weights of smokers and of non-smokers. The difference increases with age so that men over 40 years who have never smoked are on average 13 lb (5·9 kg) heavier than smokers. Even so, smokers are about 15 lb (6·8 kg) heavier than the weight standard considered desirable by the Metropolitan Life Insurance Company, while non-smokers are nearly 30 lb (13·6 kg) heavier.About 20% of the men are attempting to give up the smoking habit. Ex-smokers who have given up smoking for more than eight years approach the body weight of men of the same age who have never smoked.Many reports have been published on the health consequences of smoking and of obesity. Because smoking and obesity are inversely related studies of the interrelation of these two health hazards and of their relative importance are needed.     

Main chain hydrogen bond interactions in the binding of proline-rich gluten peptides to the celiac disease-associated HLA-DQ2 molecule

Binding of peptide epitopes to major histocompatibility complex proteins involves multiple hydrogen bond interactions between the peptide main chain and major histocompatibility complex residues. The crystal structure of HLA-DQ2 complexed with the alphaI-gliadin epitope (LQPFPQPELPY) revealed four hydrogen bonds between DQ2 and peptide main chain amides. This is remarkable, given that four of the nine core residues in this peptide are proline residues that cannot engage in amide hydrogen bonding. Preserving main chain hydrogen bond interactions despite the presence of multiple proline residues in gluten peptides is a key element for the HLA-DQ2 association of celiac disease. We have investigated the relative contribution of each main chain hydrogen bond interaction by preparing a series of N-methylated alphaI epitope analogues and measuring their binding affinity and off-rate constants to DQ2. Additionally, we measured the binding of alphaI-gliadin peptide analogues in which norvaline, which contains a backbone amide hydrogen bond donor, was substituted for each proline. Our results demonstrate that hydrogen bonds at P4 and P2 positions are most important for binding, whereas the hydrogen bonds at P9 and P6 make smaller contributions to the overall binding affinity. There is no evidence for a hydrogen bond between DQ2 and the P1 amide nitrogen in peptides without proline at this position. This is a unique feature of DQ2 and is likely a key parameter for preferential binding of proline-rich gluten peptides and development of celiac disease.     

Analysis of covalently bound polyketide intermediates on 6-deoxyerythronolide B synthase by tandem proteolysis-mass spectrometry

Polyketide natural products are biosynthesized via successive chain-elongation events mediated by elaborate protein assemblies. Facile detection of protein-bound intermediates in these systems will increase our understanding of enzyme reactivity and selectivity. We have developed a tandem proteolysis/mass spectrometric method for monitoring substrate loading and elongation in 6-deoxyerythronolide B synthase (DEBS), responsible for production of the macrolide precursor to erythromycin. Information regarding ketosynthase loading and polyketide unit elongation is readily acquired without need for complex protein or small molecule labels. A panel of structurally related substrates is evaluated through competition experiments and kinetic assays using LC-MS to resolve closely related species. Strong stereochemical effects are observed for ketosynthase substrate specificity. Semiquantitative kinetic analyses allow the resolution of the effects of structural and stereochemical changes on the individual ketosynthase-catalyzed steps of acyl-enzyme formation and polyketide chain extension.     

Biochemical analysis of the substrate specificity of the beta-ketoacyl-acyl carrier protein synthase domain of module 2 of the erythromycin polyketide synthase

The beta-ketoacyl-acyl carrier protein synthase (KS) domain of the modular 6-deoxyerythronolide B synthase (DEBS) catalyzes the fundamental chain building reaction of polyketide biosynthesis. The KS-catalyzed reaction involves two discrete steps consisting of formation of an acyl-enzyme intermediate generated from the incoming acylthioester substrate and an active site cysteine residue, and the conversion of this intermediate to the beta-ketoacyl-acyl carrier protein product by a decarboxylative condensation with a paired methylmalonyl-SACP. We have determined the rate constants for the individual biochemical steps by a combination of protein acylation and transthioesterification experiments. The first-order rate constant (k(2)) for formation of the acyl-enzyme intermediate from [1-(14)C]-(2S,3R)-2-methyl-3-hydroxypentanoyl-SNAC (2) and recombinant DEBS module 2 is 5.8 +/- 2.6 min(-)(1), with a dissociation constant (K(S)) of 3.5 +/- 2.8 mM. The acyl-enzyme adduct was formed at a near-stoichiometric ratio of approximately 0.8:1. Transthioesterification between unlabeled diketide-SNAC 2 and N-[1-(14)C-acetyl]cysteamine gave a k(exch) of 0.15 +/- 0.06 min(-)(1), with a K(m) for HSNAC of 5.7 +/- 4.9 mM and a K(m) for 2 of 5.3 +/- 0.9 mM. Under the conditions that were used, k(exch) was equal to k(-)(2), the first-order rate constant for reversal of the acyl-enzyme-forming reaction. Since the rate of the decarboxylative condensation is much greater that the rate of reversion to the starting material (k(3) > k(-)(2)), formation of the acyl-enzyme adduct is effectively irreversible, thereby establishing that the observed value of the specificity constant (k(cat)/K(m)) is solely a reflection of the intrinsic substrate specificity of the KS-catalyzed acyl-enzyme-forming reaction. These findings were also extended to a panel of diketide- and triketide-SNAC analogues, revealing that some substrate analogues that are not converted to product by DEBS module 2 form dead-end acyl-enzyme intermediates.     

The acyltransferase homologue from the initiation module of the R1128 polyketide synthase is an acyl-ACP thioesterase that edits acetyl primer units

Type II polyketide synthases (PKSs) synthesize polyfunctional aromatic polyketides through iterative condensations of malonyl extender units. The biosynthesis of most aromatic polyketides is initiated through an acetate unit derived from decarboxylation of malonyl-acyl carrier protein (ACP). Modification of this primer unit represents a powerful method of generating novel polyketides. We have demonstrated that recombination of the initiation module from the R1128 PKS with heterologous elongation modules afforded regioselectively modified polyketides containing alternative primer units. With the exception of the role of the acyltransferase homologue ZhuC, the catalytic cycle of the initiation module has been well explored. ZhuC, along with the ketosynthase III homologue ZhuH and the ACP(p) ZhuG, is essential for the in vivo biosynthesis of aromatic polyketides derived from non-acetate primer units. Here we have studied the role of ZhuC using PKS proteins reconstituted in vitro. We show that the tetracenomycin (tcm) minimal PKS can be directly primed with non-acetate acyl groups. In the presence of approximately 10 microM hexanoyl-ZhuG or approximately 100 microM hexanoyl-CoA, the tcm minimal PKS synthesized hexanoyl-primed analogues of octaketides SEK4 and SEK4b, as well as acetate-primed decaketides SEK15 and SEK15b at comparable levels. Addition of ZhuC abolished synthesis of the acetate-primed decaketides, resulting in exclusive synthesis of the hexanoyl-primed octaketides. In the absence of alternative acyl donors, ZhuC severely retarded the activity of the tcm minimal PKS. The editing capabilities of ZhuC were directly revealed by demonstrating that ZhuC has 100 times greater specificity for acetyl- and propionyl-ACP as compared to hexanoyl- and octanoyl-ACP. Thus, by purging the acetate primer units that otherwise dominate polyketide chain initiation, ZhuC (and presumably its homologues in other PKSs such as the doxorubicin and frenolicin PKSs) allows alternative primer units to be utilized by the elongation module in vivo. The abilities of other alkylacyl primer units to prime the tcm minimal PKS were also investigated in this report.