Biomedical subjects

T M Huang

Publications and source records attributed to T M Huang.

23 records · Page 2Linked to original sources

PubMed1982

Involvement of lysine residue in the nucleotide binding of pigeon liver malic enzyme: modification with affinity label periodate-oxidized NADP.

1. Periodate-oxidized NADP, a competitive inhibitor of malic enzyme with respect to NADP, inactivate the enzyme in mild conditions. 2. The inactivation is due to the modification of an essential lysine residue. 3. Two molecules of reagent were found to be incorporated into the enzyme tetramer after extensive modification. 4. Complete protection of malic enzyme from the oxidized NADP inactivation was afforded by NADP and its analogues. 5. The modified enzyme showed increased apparent Michaelis constant for the nucleotide coenzymes but the maximum velocity was decreased. 6. The binding between the modified enzyme and NADPH was impaired.

Adenosine Diphosphate↗

PubMed1981

Modification of essential arginine residues of pigeon liver malic enzyme.

The reaction of pigeon liver malic enzyme (L-malate:NADP+ oxidoreductase (oxaloacetate-decarboxylating), EC 1.1.1.40) with dicarbonyl compounds (2,3-butanedione, methylglyoxal, 2,4-pentanedione, and phenylglyoxal) resulted in a rapid loss of its enzymatic activity. The inactivation showed pseudo-first-order kinetics for all the dicarbonyls studied. All the log (pseudo-first-order rate constants) vs. log (dicarbonyl concentration) plots had slopes of near one, indicating approx. 1 : 1 reagent-active site complexes. Butanedione inactivation was reversible and was buffer-dependent. Pentanedione-modified enzyme showed a new absorption peak at 310 nM. NADP could completely protect the enzyme from inactivation. Oxaloacetate, ADP, AMP, NMN and adenosine were also effective in protection. Complete inactivation of the enzyme was accompanied by a loss of about six arginine residues per enzyme monomer. Butanedione-modified enzyme still bound NADPH as shown by fluorescence titration, nor was it binding with NADP impaired as determined by equilibrium gel filtration. The arginine residues, therefore, do not function in the coenzyme binding. However, the binding between the modified enzyme and [14C]malate was significantly decreased. These results led us to conclude that the arginine residues of malic enzyme are involved in the binding of the carboxyl group of substrate malate.

Animals↗

PubMed1980

Involvement of tyrosyl residues in the substrate binding of pigeon liver malic enzyme.

The reactions of pigeon liver malic enzyme (L-malate:NADP+ oxidoreductase (oxaloacetate-decarboxylating), EC 1.1.1.40) with tetranitromethane and N-acetylimidazole have been investigated to obtain information about the functional role of tyrosine residues in this enzyme. Incubation of the sulfhydryl-masked enzyme with tetranitromethane or N-acetylimidazole caused a time-dependent loss of all enzymatic activities of this enzyme. The absorption spectra of both the nitrated and acetylated enzyme indicated modification of tyrosine residues. The enzymatic activity of the acetylated enzyme was reversed by hydroxylamine. No amino group modification was observed. Preincubation of the enzyme with dicarboxylate substrate (or inhibitor), nucleotide coenzyme and divalent metal ions protected the enzyme against these reagents. The acetylated enzyme showed different kinetic properties from the native enzyme. The apparent Michaelis constants for malate and oxaloacetate increase by 2-5-fold. The binding between acetylated enzyme and NADPH was not abolished. These results strongly suggest the involvement of tyrosine residues in the dicarboxylic acid binding of malic enzyme.

Acetylation↗

PubMedDate not supplied

Oxidation and cleavage of 3-aminopyridine adenine dinucleotide phosphate with periodate.

Treatment of 3-aminopyridine adenine dinucleotide phosphate with sodium periodate in the neutral pH resulted in oxidation of the ribose linked to 3-aminopyridine and cleavage of the dinucleotide into adenosine- and 3-aminopyridine-containing moieties. Separation of these moieties was afforded by thin-layer chromatography, high-performance liquid chromatography, and fast protein liquid chromatography. From fast atom bombardment mass spectra and nuclear magnetic resonance spectra, the adenosine-containing moiety was identified as 2'-phosphoadenosine 5'-phosphate while the aminopyridine moiety was present in a mixture of the hydrated 3-aminopyridine mononucleotide/nucleoside dialdehyde. Separation of the completely oxidized product by Pharmacia fast protein liquid chromatography gave three major peaks corresponding to 2'-phosphoadenosine 5'-phosphate, 2'-phosphoadenosine 5'-diphosphate and oxidized 3-aminopyridine nucleoside, with minor amount of oxidized 3-aminopyridine mononucleotide. Thus the oxidized 3-aminopyridine adenine dinucleotide phosphate was shown to cleave by two pathways: it may either undergo beta-elimination to give 2'-phosphoadenosine 5'-diphosphate and oxidized 3-aminopyridine nucleoside; or the phosphodiester linkage may be hydrolyzed to give 2'-phosphoadenosine 5'-phosphate and oxidized 3-aminopyridine mononucleotide. The latter compound may further undergo beta-elimination and eventually give oxidized 3-aminopyridine nucleoside. Hydrolysis could be prevented by storing the sample as lyophilized powder, while beta-elimination was diminished by lowering the storage temperature. We found that the lyophilized powder of oxidized 3-aminopyridine adenine dinucleotide phosphate can be stored at -50 degrees C for several months with minimum decomposition.

Chromatography, High Pressure Liquid↗

PubMedDate not supplied

Sentinel surveillance for enterovirus 71, Taiwan, 1998.

Outbreaks of enterovirus 71 have been reported around the world since 1969. The most recent outbreak occurred in Taiwan during April-July 1998. This hand, foot, and mouth disease epidemic was detected by a sentinel surveillance system in April at the beginning of the outbreak, and the public was alerted.

Disease Outbreaks↗