Search PubMed⌕ Search

Biomedical subjects

J M Manning

Publications and source records attributed to J M Manning.

At least 127 records · Page 7Linked to original sources
PubMed1982

Inactivation of pyridoxal phosphate enzymes by gabaculine. Correlation with enzymic exchange of beta-protons.

Gabaculine, 5-amino-1,3-cyclohexadienylcarboxylate, is a very efficient enzyme-activated inhibitor of gamma-aminobutyrate transaminase (Rando, R. R. (1977) Biochemistry 16, 4604-4610). However, enzymes for which gamma-aminobutyrate is not a substrate are also inactivated by gabaculine. Thus, purified D-amino acid transaminase, L-alanine transaminase, and L-aspartate transaminase are also inactivated (Ki values of 0.1 mM, 1 mM, and 55 mM, respectively). The effects of this inhibitor on such a diverse group of enzymes appear to be related to the enzymic exchange of beta-protons of their normal substrates. L-Alanine transaminase and L-aspartate transaminase are known to catalyze such an exchange (Walter, U., Luthe, H., Gerhart, F., and Söling, H.-D. (1975) Eur. J. Biochem. 59, 395-403). D-Amino acid transaminase and gamma-aminobutyrate transaminase, which are inactivated by gabaculine, also catalyze exchange of the beta-protons of their substrates. Alanine racemase and tryptophanase, which are known not to catalyze an analogous exchange, were found to be insensitive to gabaculine. We postulate that aromatization of gabaculine, in which the beta-proton is removed, is an enzyme-catalyzed event for those pyridoxal phosphate enzymes that have a nucleophilic group at the active site to catalyze this process.

4-Aminobutyrate Transaminase↗
PubMed1982

Labeling of hemoglobin with pyridoxal phosphate.

The reaction of pyridoxal 5'-phosphate (PLP) with deoxyhemoglobin is confined to 2 residues in the beta chains, i.e. the alpha-amino group of valine 1 and the epsilon-amino group of lysine 82, both of which are located in the polyphosphate binding site. The major product is a hemoglobin in which only the two NH2-terminal amino groups are substituted (symmetric diPLPHb). It is formed by subunit rearrangement of monoPLPHb which is the initial product of the pyridoxylation under anaerobic conditions. TetraPLPHb, with substitutions at lysine 82 and valine 1 of both beta chains is found as a minor component. It results from subunit exchange of asymmetric diPLPHb consisting of one unmodified alpha beta dimer and one which is pyridoxylated at both sites. Anaerobic electrophoresis and oxygenation curves show that this reaction is readily reversed by mixing the tetrasubstituted derivative with unmodified hemoglobin.

Amino Acids↗
PubMed1982

Transaminases.

Explore the source record for details and available documents.

Chemical Phenomena↗
PubMed1981

Different modes of action of inhibitors of bacterial D-amino acid transaminase. A target enzyme for the design of new antibacterial agents.

D-Amino acid transaminase from Bacillus sphaericus shows a deuterium kinetic isotope effect (VH/VD) between 2 and 3 in the transamination of alpha-protio- or alpha-deuterio-D-alanine and alpha-ketoglutarate, suggesting that alpha-proton abstraction is at least partially rate-limiting for this reaction. This transaminase also catalyzes a beta-elimination reaction with substrates such as beta-fluoroalanine with no detectable deuterium isotope effect (VH/BD = 1). These results, taken together with previous work (Soper, T. S., and Manning, J. M. (1978) Biochemistry 17, 3377-3384) suggest that the rate-limiting step in the beta-elimination reaction is solvolysis of an alpha-aminoacrylate-pyridoxal-P Schiff's base intermediate. D-Cycloserine is an active site titrant of D-amino acid transaminase. Inactivation by cycloserine can be completely reversed by dialysis against pyridoxal phosphate at neutral pH. Gabaculine is also an efficient inhibitor of this enzyme and possesses some antibacterial activity. The latter two inhibitors probably act by sequestration of the coenzyme rather than by alkylation of the protein as with the beta-halo derivatives of D-alanine.

Alanine↗
PubMed1980

Oxygen-linked binding sites for inorganic anions to hemoglobin.

A hemoglobin hybrid (alpha 2c beta 2 Prov) in which the alpha chains have NH2-terminal residues that have been blocked specifically by carbamylation and beta chains that have been derived from hemoglobin Providence I (beta 82 Lys leads to Asn) was prepared. This derivative shows a small but significant dependence of its oxygen equilibrium curve on the concentration of chloride, phosphate, or nitrate. These data were compared with oxygen-linked anion binding to hemoglobins A and Providence, and to the carbamylated hybrid, alpha 2c beta 2, by fitting equations to the data with the use of MULTIFIT II, a nonlinear curve-fitting program. Dependence of the anion dissociation constants from deoxygenated (KD) and fully oxygenated (Ko) hemoglobins upon the mathematical model is described. The data provide further support that Val-1 (alpha) and Lys-82 (beta) of hemoglobin are major, oxygen-linked binding sites for small inorganic anions and suggested that a third oxygen-linked site may also be present.

Anions↗
PubMed1980

Reactivity of the amino groups of carbonmonoxyhemoglobin S with glyceraldehyde.

The inhibition of erythrocyte sickling in vitro by glyceraldehyde has been shown previously to result from a reduced gelation of deoxyhemoglobin S. Accordingly, the sites of Schiff base formation of the sugar aldehyde with hemoglobin have been determined by peptide of the protein after treatment of CO-saturated sickle cells with 10 mM [14C]glyceraldehyde for 90 min and reduction with NaBH4. About 23% of the glyceraldehyde incorporated into hemoglobin was present at Val-1(beta) with very little present at Val-1(alpha) (less than 5%. The distribution of [14C]glyceraldehyde between the hemoglobin chains was 60% in the beta chains and 40% in the alpha chains. The reactive lysine residues of the beta chain were Lys-82, Lys-59, and Lys-120 (45%, 20%, and 16% of the total 14C in the beta chains, respectively). The most reactive lysine residue of the alpha chain was Lys-16 where 75% of the total [14C]glyceraldehyde was present. The limited number of sites reactive with glyceraldehyde indicate some type of selectivity in the reaction of sugar aldehydes with hemoglobin.

Amino Acids↗
PubMed1980

Mouse peritoneal macrophages release leukotriene C in response to a phagocytic stimulus.

Mouse peritoneal macrophages that had ingested zymosan particles released a polar metabolite of arachidonic acid possessing slow-reacting substance activity in the guinea pig ileum assay. The metabolite was purified by solvent extraction, Sephadex G-25 column chromatography. The purified metabolite absorbed light at 280 nm and contained a free amino group. When macrophages were preincubated overnight with [3H]arachidonic acid, [35H]cysteine, or [14C]glutamic acid, each radiolabel was incorporated into the compound. Direct amino acid analysis revealed glycine, glutamic acid, and cysteine at molar ratios of 0.97:1.00:0.82. The above data were consistent with the structure of leukotriene C, an adduct of arachidonic acid and glutaathione. Quantification of the leukotriene C based on incorporation of [3H]arachidonic acid or amino acid analysis indicated that 6 X 10(7) macrophages (3.6 mg of cell protein) released 7.5 nmol after a maximal phagocytic stimulus. The purified leukotriene C had a slow reacting substance activity of 11,500 units/nmol (1 unit has the activity of 5 ng of histamine in a guinea pig ileum contraction assay).

Amino Acids↗
PubMed1980

Measurement of the carbamylation kinetics and antisickling mechanism in hemoglobin S blood.

The kinetics of HbS carbamylation in whole blood have been investigated under conditions anticipated in extracorporeal treatment systems. The reaction was well represented by a bimolecular, irreversible, second-order mechanism, and the overall carbamylation rate was enhanced by increasing the temperature and decreasing the pH and PO2. An expression was developed to predict the carbamylation rate for a range of experimental conditions. The relative amount of beta chain carbamylation was increased for those conditions under which the overall carbamylation rate was lowered, i.e., lower temperature, higher PO2, and higher pH. Morphological examination of cells with predominantly beta chain carbamylation showed that the antisickling effect, as measured by this technique, could be accounted for entirely by an increase in the oxygen affinity. Although this observation does not exclude an effect independent of change in the oxygen affinity of carbamylated hemoglobin, such an effect, if it occurs, is not detectable by this method. The results of this study were used to design a reaction vessel for an extracorporeal treatment system for sickle cell anemia patients.

Carbamates↗
PubMed1978

Effects of glyceraldehyde on the structural and functional properties of sickle erythrocytes.

The d- and l-isomers of glyceraldehyde are equally effective in the inhibition of SS erythrocyte sickling in vitro. The following compounds at a concentration of 20 mM were ineffective in inhibiting sickling: glyceraldehyde-3-phosphate, d-erythrose, d-ribose, d-fructose, d-glucose, d-sucrose, dihydroxyacetone, and methylglyoxal. Glyceraldehyde does not reverse the sickling of cells in the deoxy state. The properties of purified hemoglobin after treatment with glyceraldehyde and of the hemoglobin isolated from treated cells are very similar; these results suggest that glyceraldehyde itself is the reactive species within the erythrocyte. Erythrocyte glutathione is decreased by treatment in vitro with the aldehyde. Relatively high concentrations of glyceraldehyde (50 mM) lead to a small amount (3%) of cross-linking between hemoglobin monomers as well as to some cross-linking of erythrocyte membrane proteins. Lower concentrations of dl-glyceraldehyde (5-20 mM), which reduce the sickling of erythrocytes in vitro, lead to proportionally less cross-linking of hemoglobin. Cells that have been treated with those concentrations of the aldehyde show little change in their osmotic fragility, exhibit improved filtration properties, and have a lowered viscosity.

Anemia, Sickle Cell↗
PubMed1977

Inactivation of bacterial D-amino acid transaminase by beta-chloro-D-alanine.

Purified D-amino acid transaminase from Bacillus sphaericus catalyzes an alpha,beta elimination from the D isomer of beta-chloroalanine to yield equivalent amounts of pyruvate, chloride, and ammonia; the L isomer of chloroalanine is not a substrate for this transaminase. During the beta elimination there is a synchronous loss in enzyme activity; the Kinact for beta-chloroalanine was estimated to be about 10 micrometers. The alpha-aminoacrylate-Schiff base intermediate formed after beta elimination of chloride ion is probably the key intermediate that partitions between one inactivation event for every 1500 turnovers. In the presence of D-alanine and alpha-ketoglutarate, which are good substrates for the transaminase activity of this enzyme, beta-chloroalanine is a potent, competitive inhibitor (K1 = 10 micrometers) with D-alanine and a weak, uncompetitive inhibitor with alpha-ketoglutarate.

Alanine↗
PubMed1977

Inactivation of bacterial D-amino acid transaminases by the olefinic amino acid D-vinylglycine.

D-Vinylglycine (2-amino-3-butenoate) functions as a transamination substrate and irreversible inactivator of the homogeneous pyridoxal phosphate-dependent D-amino acid transaminases from Bacillus subtilis and Bacillus sphaericus. In the absence of alpha-ketoglutarate as co-substrate, vinyl-glycine causes little if any inactivation of either enzyme; in the presence of excess alpha-ketoglutarate, both enzymes are inactivated with pseudo-first order kinetics. The limiting rate constant for inactivation of the B. sphaericus enzyme is 1.9 min-1, for the B. subilis enzyme it is 0.36 min-1. The number of catalytic events before inactivation is about 450 for the B. sphaericus enzyme and about 800 for the B. subtilis enzyme; that is, about 0.2% inactivation in each catalytic cycle for the former enzyme and 0.15% for the latter. Comparisons are made with the L-aspartate amino-transferase from pig heart which is inactivated completely in one catalytic cycle and the L-alanine aminotransferase which is not inactivated in many cycles. Comparisons are also made between the likely mode of D-transaminase inactivation produced by vinylglycine and the mode of inactivation induced by beta-chloro-D-alanine.

Amino Acids↗
PubMed1977

Inhibition of erythrocyte sickling in vitro by DL-glyceraldehyde.

Concentrations of DL-glyceraldehyde between 5 and 20 mM reduce the sickling of S/S erythrocytes even in the complete absence of oxygen; at 10 mM glyceraldehyde the increase in the number of normal cells ranges from 20 to 40%. The inhibition of sickling was both concentration- and time-dependent and was not reversed by repeated washings with buffer. Incubation of erythrocytes with increasing concentrations of glyceraldehyde resulted in only a small increase in the oxygen affinity, a moderate reduction in the Hill coefficient, a substantial increase in the minimum gelling concentration, and modification of up to two lysine residues per hemoglobin molecule.

Anemia, Sickle Cell↗
PubMed1976

Reactivity of cyanate with valine-1 (alpha) of hemoglobin. A probe of conformational change and anion binding.

The 3-fold increase in the carbamylation rate of Val-1 (alpha) of hemoglobin upon deoxygenation described earlier is now shown to be a sensitive probe of conformational change. Thus, whereas this residue in methemoglobin A is carbamylated at the same rate as in liganded hemoglobin, upon addition of inositol hexaphosphate its carbamylation rate is enhanced 30% as much as the total change in the rate between the CO and deoxy states. For CO-hemoglobin Kansas in the presence of the organic phosphate, the relative increase in the carbamylation rate of this residue is about 50%. These results indicate that methemoglobin A and hemoglobin Kansas in the presence of inositol hexaphosphate do not assume a conformation identical with deoxyhemoglobin but rather form either a mixture of R and T states or an intermediate conformation in the region around Val-1 (alpha). Studies on the mechanism for the rate enhancement in deoxyhemoglobin suggest that the cyanate anion binds to groups in the vicinity of Val-1 (alpha) prior to proton transfer and carbamylation of this NH2-terminal residue. Thus, specific removal with carboxypeptidase B of Arg-141 (alpha), which is close to Val-1 (alpha) in deoxyhemoglobin, abolishes the enhancement in carbamylation. Chloride, which has the same valency as cyanate, is a better competitive inhibitor of the carbamylation of deoxyhemoglobin (Ki = 50 mM) compared with liganded hemoglobin. Nitrate and iodide are also effective inhibitors of the carbamylation of Val-1 (alpha) of deoxyhemoglobin (Ki = 35 mM); inorganic phosphate, sulfate, and fluoride are poor competitive inhibitors. The change in pKa of Val-1 (alpha) upon deoxygenation may be due to its differential interaction with chloride.

Anions↗