Vasovagal syncope and anaesthetic practice.

We surveyed anaesthetists working in North-West England and in North Wales concerning episodes of vasovagal syncope encountered in their practice. Eighty-eight anaesthetists described 109 such events occurring in either patients or their relatives and the estimated frequency of syncope was 1 in 5000 anaesthetic episodes. The patient syncopal episodes were triggered by venous cannulation in 16 instances and regional or local techniques in 20 instances. Thirty-three of the 53 patients were in the upright position when syncope occurred. Thirty-nine of the 56 relatives were male partners of female patients and four of these partners suffered some morbidity. The results of the survey are consistent with our current knowledge of the pathophysiology of vasovagal syncope, which is summarized, and also highlight the common anaesthetic scenarios where fainting is most likely to occur. Given this information anaesthetists will be in a better position to avoid such potentially harmful episodes in the future.

Slow-binding inhibition of NAD+ glycohydrolase by arabino analogues of beta-NAD.

Modifications at the 2'-position of the nicotinamide-ribosyl moiety influence dramatically the nature of the interactions of the modified beta-NAD+ with calf spleen NAD+ glycohydrolase (EC 3.2.2.6), an enzyme that cleaves the nicotinamide-ribose bound in NAD(P)+. Nicotinamide arabinoside adenine dinucleotide (ara-NAD+) and nicotinamide 2'-deoxy-2'-fluoroarabinoside adenine dinucleotide (araF-NAD+) are not hydrolyzed at measurable rates and are the first documented examples of reversible slow binding inhibitors of this class of enzyme. The kinetic data obtained are consistent with both slow kon and koff rate constants in the formation of an enzyme-inhibitor complex, i.e. the association rate constants are about 10(4) and 10(6) slower than diffusion rates, respectively, for araF-NAD+ and ara-NAD+, and the half-life of the complex is about 3-10 min for both analogues. The kinetic model does not account for a slow turnover of an ADP-ribosyl-enzyme intermediary complex. AraF-NAD+ is one of the most potent inhibitors described for NAD+ glycohydrolase.

Purification, immunochemical characterization, and immunohistochemical localization of rat hepatic aryl sulfotransferase IV.

Aryl sulfotransferases catalyze the formation of sulfuric acid esters from a diverse group of endogenous and xenobiotic organic chemicals. The isoenzyme of aryl sulfotransferase in livers of male Sprague-Dawley rats that exhibits the most varied substrate specificity is aryl sulfotransferase IV. A new method for the purification to homogeneity of aryl sulfotransferase IV was developed that, when compared with previously described procedures, provided a greater than 10-fold increase in total yield of enzyme/g of tissue. Homogeneous aryl sulfotransferase IV was used to prepare polyclonal antibodies in male New Zealand White rabbits. Results of immunochemical analyses demonstrated that these antibodies reacted with only a single protein in rat hepatic 100,000 x g supernatant fractions and, further, that the immunoreactive protein had the isoelectric point and subunit molecular mass characteristic of aryl sulfotransferase IV. Immunohistochemical analyses demonstrated that aryl sulfotransferase IV is present in hepatocytes throughout the liver, although centrilobular cells contain a significantly greater (p less than 0.01) amount of aryl sulfotransferase IV than do either midzonal or periportal cells, in which similar levels of the enzyme are found.

p-Nitrophenyl and cholesteryl-N-alkyl carbamates as inhibitors of cholesterol esterase.

p-Nitrophenyl and cholesteryl-N-alkyl carbamates are good inhibitors of porcine pancreatic cholesterol esterase-catalyzed hydrolysis of p-nitrophenyl butyrate. p-Nitrophenyl-N-butyl and N-octyl carbamates (compounds 1 and 2, respectively) are potent active site-directed irreversible inhibitors of this enzyme. The inhibition of cholesterol esterase by compound 1 or 2 shows saturation kinetics with increasing inhibitor concentration. The activity of cholesterol esterase in the presence of compound 1 or 2 can be protected by the competitive inhibitor, phenylboronic acid. First-order decreases in cholesterol esterase activity effected by compound 1 or 2 are also observed in the presence of taurocholate/phosphatidylcholine micelles. Dilution of the inhibited enzyme results in a gradual return of activity, the rate of which is increased in the presence of the nucleophile hydroxylamine. Hence, inhibition of cholesterol esterase-catalyzed hydrolysis of p-nitrophenyl butyrate by compound 1 or 2 in the aqueous or micellar phase occurs via a carbamyl-cholesterol esterase mechanism. The turnover of the butyl carbamylenzyme is increased in the presence of micelles, which indicates that the micelles have a direct effect on the catalytic activity of the enzyme. However, this effect is dependent on the structure of the substrate as the turnover of the octyl carbamylenzyme is unaffected in the presence of micelles. A comparison of the second-order rate constants for the inhibition of cholesterol esterase by compound 1 or 2 indicates that the octyl derivative is the more potent inhibitor. Cholesteryl-N-alkyl carbamates do not carbamylate cholesterol esterase but instead act as reversible inhibitors. This is due to the stability of cholesteryl carbamates relative to p-nitrophenyl carbamates.

Phenyl-n-butylborinic acid is a potent transition state analog inhibitor of lipolytic enzymes.

The cholesterol esterase and lipoprotein lipase catalyzed hydrolyses of the water-soluble substrate p-nitrophenyl butyrate are competitively inhibited by butaneboronic acid and phenylboronic acid. Phenyl-n-butylborinic acid has been synthesized and characterized as an ultrapotent transition state analog inhibitor: Ki = 2.9 +/- 0.6 nM and 1.7 +/- 0.3 microM for the cholesterol esterase and lipoprotein lipase reactions, respectively. These results are interpreted in terms of transition state structure and stabilization.

Effects of deuterium substitution alpha and beta to the reaction centre, 18O substitution in the leaving group, and aglycone acidity on hydrolyses of aryl glucosides and glucosyl pyridinium ions by yeast alpha-glucosidase. A probable failure of the antiperiplanar-lone-pair hypothesis in glycosidase catalysis.

Neither kcat. nor kcat./Km for five aryl alpha-D-glucopyranosides correlates with aglycone pKa, and isotope effects, described according to the convention used by Cleland [(1982) CRC Crit. Rev. Biochem. 13, 385-428], of 18(V) = 1.002 +/- 0.008, alpha D(V) = 1.01 +/- 0.04 and alpha D(V/K) = 0.969 +/- 0.035 are observed for p-nitrophenyl, and one of beta D(V) = 1.02 +/- 0.04 for phenyl alpha-D-glucopyranoside; kcat. but not kcat./Km, correlates with aglycone pKa for five alpha-D-glucopyranosyl pyridinium ions with a Brønsted coefficient of -0.61 +/- 0.06, and isotope effects of alpha D(V) = 1.22 +/- 0.02, beta D(V) = 1.13 +/- 0.01 and alpha D(V/K) = 1.018 +/- 0.046 for the 4-bromoisoquinolinium, and alpha D(V) = 1.15 +/- 0.02 and beta D(V) = 1.085 +/- 0.011 for the pyridinium salts are observed. These data require that a non-covalent event, fast in the case of the N-glycosides but slow in the case of the O-glycosides, precedes bond-breaking, and that bond-breaking involves substantial charge development on the glycone and near-perpendicularity of the C2-H bond to the planar oxocarbonium ion system. A model meeting these requirements is that the non-covalent event is a conjoint change of protein and substrate conformation which puts the pyranose ring in the 2,5B conformation of the bond-breaking transition state. This model also explains the contrast between the powerful inhibition of the enzyme by deoxynojirimycin (Ki = 23 +/- 3 microM) and feeble inhibition by castanospermine [Saul, Chambers, Molyneux & Elbein (1983) Arch. Biochem. Biophys. 221, 593-597], but is directly contrary to the predictions of Deslongchamps' 'Theory of Stereoelectronic Control' [Deslongchamps (1975) Tetrahedron 31, 2463-2490; (1983) Stereoelectronic Effects in Organic Chemistry, p. 39, Pergamon Press, Oxford].