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Biomedical subjects

D A Yost

Publications and source records attributed to D A Yost.

At least 19 recordsLinked to original sources
PubMed1996

Alcohol withdrawal syndrome.

Hundreds of thousands of significant alcohol withdrawal episodes are encountered by primary care physicians every year. If the situation is appreciated at an early stage, most patients can be managed successfully on an outpatient basis with benzodiazepines. Patients with seizures, concurrent medical illnesses and severe withdrawal signs should be hospitalized. Fewer than 5 percent of patients withdrawing from alcohol progress to delirium tremens. Mortality from delirium tremens has been reduced to less than 5 percent of patients, through early diagnosis, supportive nursing care, treatment of coexisting medical conditions and aggressive pharmacologic therapy. Patients with a history of multiple detoxification episodes are more likely to experience seizures and severe withdrawal symptoms.

Adult↗
PubMed1989

Clinical safety of aspartame.

Aspartame is a synthetic sweetener commonly used in soft drinks and many foods. Even with high doses, the metabolites of this sweetener do not accumulate in toxic amounts. To date, no definite symptom complex has been connected with aspartame, and it is considered safe for use in all populations, including diabetics, phenylketonuric heterozygotes and pregnant women.

Aspartame↗
PubMed1985

Amino acid-specific ADP-ribosylation. Sensitivity to hydroxylamine of [cysteine(ADP-ribose)]protein and [arginine(ADP-ribose)]protein linkages.

Hydroxylamine stability has been used to classify (ADP-ribose)protein bonds into sensitive and resistant linkages, with the former representing (ADP-ribose)glutamate, and the latter, (ADP-ribose)arginine. Recently, it was shown that cysteine also serves as an ADP-ribose acceptor. The hydroxylamine stability of [cysteine([32P]ADP-ribose)]protein and [arginine([32P] ADP-ribose)]protein bonds was compared. In transducin, pertussis toxin catalyzes the ADP-ribosylation of a cysteine residue, whereas choleragen (cholera toxin) modifies an arginine moiety. The (ADP-ribose)cysteine bond formed by pertussis toxin was more stable to hydroxylamine than was the (ADP-ribose)arginine bond formed by choleragen. The (ADP-ribose)cysteine bond apparently represents a third class of ADP-ribose bonds. Pertussis toxin ADP-ribosylates the inhibitory guanyl nucleotide-binding regulatory protein (Gi) of adenylate cyclase, whereas choleragen modifies the stimulatory guanyl nucleotide-binding regulatory protein (Gs). These (ADP-ribose)protein linkages are identical in stability to those formed in transducin by the two toxins, consistent with the probability that cysteine and arginine are modified in Gi and Gs, respectively. Bonds exhibiting differences in hydroxylamine-stability were found in membranes from various non-intoxicated mammalian cells following incubation with [32P]NAD, which may reflect the presence of endogenous NAD:protein-ADP-ribosyl-transferases.

Adenosine Diphosphate Ribose↗
PubMed1985

Detection of NAD:arginine ADPribosyltransferases in animal tissues using 125I-labeled 1-(p-hydroxyphenyl) 2-guanidinoethane as ADPribose acceptor.

125I-labeled 1-(p-hydroxyphenyl) 2-guanidinoethane (N-guanyltyramine), previously used to assay for the bacterial toxin choleragen (Mekalanos, J.J., Collier, R.J. and Romig, W.R. (1979) J. Biol. Chem. 254, 5849-5854) was utilized to identify NAD:arginine ADPribosyltransferases in animal tissues. The use of this radiolabelled ADPribose acceptor, rather than radiolabelled NAD, would bypass the problem posed by the almost ubiquitous presence of enzymes that degrade NAD. With a homogeneous ADPribosyltransferase from turkey erythrocytes, NAD and 125I-labeled guanyltyramine as ADPribose acceptor, formation of ADPribosyl 125I-guanyltyramine was linear with time and enzyme concentration. The product was indistinguishable on both thin-layer and high-performance liquid chromatography from that formed by choleragen. Using 125I-guanyltyramine, ADPribosyltransferase activity was also demonstrated in crude turkey erythrocyte cytosolic and membrane fractions. When rat liver was fractionated, apparent activity was detected primarily in the microsomes. The NAD-dependent product of the microsomal reaction was, however, distinguished from the turkey erythrocyte transferase product by thin-layer and DEAE-Sephadex chromatography; this product had a retention time identical to that of free 125I on high-performance liquid chromatography. In addition to NAD, the microsomal deiodinase activity was supported by NADH, NADP and NADPH. Phenyl boronate selectively bound ADPribosyl 125I-guanyltyramine and other metabolites of 125I-guanyltyramine which were formed by microsomes in a NAD-dependent process. These metabolites were distinguished from ADPribosyl 125I-guanyltyramine by high-performance liquid chromatography. These results indicate that in some cases, for example, turkey erythrocyte cytosolic and membrane fractions, 125I-guanyltyramine can be used to quantify ADPribosyltransferases in crude mixtures, whereas in others, for example, rat liver microsomes, high-performance liquid chromatographic analysis must be used to identify products.

ADP Ribose Transferases↗
PubMed1985

Studies of self-inactivation of bovine seminal fluid NAD glycohydrolase.

Bovine seminal fluid NAD glycohydrolase (NADase) was observed to be rapidly inactivated during catalytic hydrolysis of the substrate NAD. The first-order rate constant for the self-inactivation process was independent of enzyme concentration. The enzyme self-inactivation was a turnover-related process and the number of moles of NAD hydrolyzed required for inactivation was proportional to the enzyme concentration. A number of dinucleotides serving as substrates for the enzyme also promoted self-inactivation. The self-inactivation was an irreversible process having a different rate-limiting step from NAD hydrolysis and was not related to the reversible binding of products and substrate-competitive inhibitors. Modification of arginine residues of the enzyme resulted in the loss of NAD hydrolase activity with no differential effect on the self-inactivation process.

Animals↗
PubMed1985

Sjögren-Larsson syndrome: delta 5-and delta 6-fatty acid desaturases in skin fibroblasts.

Cultured skin fibroblasts from two patients with Sjögren-Larsson syndrome (SLS) and from a normal control were analyzed for trienoic and tetraenoic fatty acids. In addition, we assayed desaturation of [1-14C]linoleic acid in cells from four patients and four controls. There was no significant effect of the disease on the composition of polyunsaturated fatty acids or on the rate of linoleic acid desaturation in fibroblasts. The results indicate the presence of delta 5- and delta 6-fatty acid desaturases in cells from SLS patients.

Adult↗
PubMed1984

Increased phosphorylation of myosin light chain kinase after an increase in cyclic AMP in intact smooth muscle.

The role of cyclic adenosine monophosphate-mediated phosphorylation of myosin light chain kinase in relaxing smooth muscle was examined. The kinase was immunoprecipitated from tissue extracts and the phosphate content was determined. The addition of forskolin to resting or methacholine-contracted muscles resulted in an increase in myosin light chain kinase phosphorylation of myosin light chain kinase is one of the reactions in the process by which cyclic adenosine monophosphate causes relaxation of smooth muscle.

Animals↗
PubMed1983

Activation by thiol of the latent NAD glycohydrolase and ADP-ribosyltransferase activities of Bordetella pertussis toxin (islet-activating protein).

Pertussis toxin (islet-activating protein) activates adenylate cyclase in susceptible cells by ADP-ribosylating an inhibitory component of the cyclase system. This toxin, assayed in a cell-free system in the presence of high concentrations of thiol, catalyzed the hydrolysis of NAD to ADP-ribose and nicotinamide. This NAD glycohydrolase activity co-chromatographed on Sephacryl G-200 in 6.5 M urea, pH 3.2, 0.1 M glycine with the ADP-ribosyltransferase activity of the toxin, as monitored by the transfer of [32P]ADP-ribose from [32P]NAD to a 41,000-Da protein in NG108-15 neuroblastoma X glioma hybrid cells. In the absence of thiol, the native holotoxin was enzymatically inactive. Following addition of 250 mM dithiothreitol to the assay, maximal enzymatic activity was evident after a delay of approximately 1 h; with 20 mM thiol, the delay was longer. The Km for NAD with the fully activated enzyme was 25 microM; the Km did not appear to vary with the extent of activation. Thiol was necessary in a cell-free system to demonstrate NAD glycohydrolase activity. When extensively washed membranes were used as a source of 41,000-Da substrate, thiol was necessary to observe ADP-ribosylation in some cases (human erythrocytes) and significantly stimulated activity in others (NG108-15 cells). In contrast to the bacterial toxins choleragen and Escherichia coli heat-labile enterotoxin that ADP-ribosylate stimulatory components of the cyclase system, pertussis toxin did not transfer ADP-ribose to low molecular weight guanidino compounds, such as arginine or agmatine.

Adenosine Diphosphate Ribose↗
PubMed1983

Amino acid-specific ADP-ribosylation.

[adenine-U-14C]ADP-ribose-agmatine and [adenine-U-14C ))ADP-ribose-histone were synthesized by an NAD:arginine ADP-ribosyltransferase from [14C]NAD and agmatine and histone, respectively. The pseudo-first order rate constants for breakdown of the two components either in 0.4 N NaOH or in 0.4 M neutral hydroxylamine were identical. Hydroxylamine treatment of [14C]ADP-ribose-agmatine or [32P]ADP-ribose-histone yielded a single radioactive product which was separated by high pressure liquid chromatography and identified as ADP-ribose-hydroxamate by the formation of a ferric chloride complex. Hydrolysis of ADP-ribose-hydroxamate with snake venom phosphodiesterase resulted in the formation of 5'-AMP, consistent with the presence of a pyrophosphate bond. Incubation of ADP-ribose-[14C]agmatine, synthesized by the ADP-ribosyltransferase from NAD and [14C]agmatine, with 0.4 M neutral hydroxylamine resulted in the release of [14C]agmatine rather than phosphoribosyl[14C]agmatine. In addition, neither NAD nor ADP-ribose reacts with hydroxylamine; i.e. there was no evidence of nucleophilic attack by hydroxylamine at the pyrophosphate bond. The ADP-ribosyl-protein linkage formed by the NAD:arginine ADP-ribosyltransferase is considerably more stable to hydroxylamine than is the ADP-ribose-glutamate bond. The presence of ADP-ribose-arginine and ADP-ribose-glutamate synthesized by the ADP-ribosyltransferase and poly(ADP-ribose) synthetase, respectively, may be the chemical basis for the "hydroxylamine-stable" and "hydroxylamine-labile" bonds described by Hilz (Hilz, H. (1981) Hoppe-Seyler's Z. Physiol. Chem. 362, 1415-1425).

ADP Ribose Transferases↗
PubMed1983

Amino acid-specific ADP-ribosylation. Evidence for two distinct NAD:arginine ADP-ribosyltransferases in turkey erythrocytes.

An NAD:arginine mono-ADP-ribosyltransferase has been purified 270,000-fold from turkey erythrocytes through a five-step chromatographic procedure to apparent electrophoretic homogeneity. Molecular weight determinations of the enzyme by sodium dodecyl sulfate-gel electrophoresis, Ultrogel AcA 54, and TSK 3000 SW gel filtration were consistent with Mr = 32,000. The purified enzyme utilized arginine, other low molecular weight guanidino compounds, and various proteins as ADP-ribose acceptors. The Km values for NAD and arginine methyl ester were 36 and 3,000 microM, respectively. Unlike another transferase purified from turkey erythrocytes (Moss, J., and Stanley, S.J. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 4809-4812), this enzyme was not activated by chaotropic salts or micromolar concentrations of histone. Thus, two distinct soluble ADP-ribosyltransferases may be present in turkey erythrocytes.

ADP Ribose Transferases↗
PubMed1983

Adenosine diphosphoribose transfer reactions catalyzed by Bungarus fasciatus venom NAD glycohydrolase.

Reactions catalyzed by purified Bungarus fasciatus venom NAD glycohydrolase were demonstrated to include ADP-ribose transfer from NAD to alcohols and to imidazole derivatives to produce a variety of ADP-ribosides. The formation of products was monitored by high performance liquid chromatography. In the enzyme-catalyzed alcoholysis of NAD, the ratio of n-alkyl-ADP-riboside formed to the hydrolytic product, ADP-ribose, increased linearly with alcohol concentration. The effectiveness of alcohols as acceptors of the ADP-ribose moiety in these reactions increased with increasing chainlength of the alcohol used. Linear positive chainlength effects extended from methanol to pentanol suggesting facilitation of these reactions by nonpolar interactions. In the methanolysis reaction, NADP, thionicotinamide adenine dinucleotide, nicotinamide-1, N6-ethenoadenine dinucleotide, and 3-acetylpyridine adenine dinucleotide were shown to be as effective as NAD as donor substrates. The NAD glycohydrolase-catalyzed ADP-ribose transfer to pyridine bases to form NAD analogs was studied at pyridine base concentrations above those determined to be saturating for the base exchange reaction. Under these conditions, the ratio of base exchange to hydrolysis of NAD was directly related to the pKa of the ring nitrogen of the pyridine base employed. In addition to alcoholysis and pyridine-base exchange reactions, the snake venom enzyme was demonstrated to catalyze an ADP-ribose transfer reaction to imidazole derivatives. Arginine methyl ester was ineffective as an ADP-ribose acceptor molecule in these reactions.

Adenosine Diphosphate Ribose↗
PubMed1983

Characterization of NAD: arginine ADP-ribosyltransferases in animal tissues.

Two NAD: arginine ADP-ribosyltransferases (transferase "A" and "B") were identified in turkey erythrocytes and purified to homogeneity. Both transferases in the presence of NAD catalyzed the ADP-ribosylation of arginine, other low molecular weight guanidino compounds and proteins. ADP-ribosyltransferase A was activated by chaotropic salt or histone. Activation was associated with the disaggregation of an inactive, rapidly sedimenting, high molecular weight species to a protomeric form of approximately 28,000 daltons; this protomer in equilibrium aggregate transition was rapidly reversible. In the presence of salt, the Km's for NAD and arginine methyl ester were 15 microM and 1.3 mM, respectively; the turnover number for the purified enzyme was approximately 9,900 mol X min-1 X mol enzyme-1. ADP-ribosyltransferase B exhibited a substrate specificity clearly distinct from that of transferase A. Transferase B had a Mr of 32,000, slightly larger than that of the transferase A protomer. The activity of transferase B was unaffected by histone and inhibited by chaotropic salts; its Km's for NAD and arginine methyl ester of 36 microM and 3 mM, respectively, were similar to those obtained with transferase A. These studies are consistent with the presence of two different NAD: arginine ADP-ribosyltransferases in turkey erythrocytes exhibiting distinct kinetic, regulatory, and physical properties.

ADP Ribose Transferases↗
PubMed1982

Studies of Bungarus fasciatus venom NAD glycohydrolase. Inhibition, modification, and transglycosidation reactions.

The properties of the NAD-binding domain of Bungarus fasciatus venom NAD glycohydrolase were investigated by a number of biochemical techniques. Inhibitor studies indicated that an intact dinucleotide was required for effective enzyme recognition. Adenosine derivatives, AMP, ADP, ATP, adenosine diphosphoribose (ADP-rib), and 2'-phosphoadenosine diphosphoribose (phospho-ADP-rib), were linear competitive inhibitors of the NADase-catalyzed reaction. Nicotinamide analogs were noncompetitive inhibitors with Ki values that varied with the nature and position of substituent groups. Selective enzyme inactivation by 2,4-pentanedione indicated the importance of a lysinyl residue for NADase activity. The importance of a carboxyl group was also indicated by the sensitivity of the NADase toward N-ethyl-5-phenyl-isoxazolium-3'-sulfonate (Woodward's Reagent K). Reagents which modified sulfhydryl, histidyl, and arginyl residues were not effective in inactivating B. fasciatus venom NADase. The purified snake venom NADase catalyzed a transglycosidation (pyridine base exchange) reaction. The functioning of a variety of substituted pyridine bases in this reaction was demonstrated by the formation of the corresponding NAD analogs. Kinetic studies of the transglycosidation reaction were consistent with the partitioning of an enzyme-ADP-rib intermediate between water and the substituted pyridine base. Concentrations of pyridine bases required for enzyme inhibition differed significantly from those needed for the pyridine base exchange reaction, suggesting two sites or two forms of the NADase differing in affinity for pyridine bases. A number of NAD analogs were also shown to be effective ribosyl donors in the transglycosidation reaction.

Adenine Nucleotides↗