BACKGROUND Homocysteine, a risk factor of cardiovascular disease, cognitive disorders, and pregnancy complications, exists at a point of metabolic convergence of several B vitamins, including vitamins B(6) and B(2) (riboflavin). Measurement of the various forms of these vitamins may be useful for the study of hyperhomocysteinemia as well as for the assessment of vitamin status. METHODS Plasma...

Several pyridoxal-phosphate-dependent enzymes can convert the bound cofactor to pyridoxamine phosphate. This conversion may be an obligatory part of the normal catalytic sequence, as with transaminases, or may be an abnormal path, inactivating the enzyme. This conversion requires protonation of the C(4)' carbon of the cofactor, which has now been shown to proceed stereospecifically and with the...

Tyrosine phenol-lyase (EC 4.1.99.2) from Citrobacter freundii has been cloned and the primary sequence deduced from the DNA sequence. From the BrCN digest of the NaBH4-reduced holoenzyme, five peptides were purified and sequenced. The amino acid sequences of the peptides agreed with the corresponding parts of the tyrosine phenol-lyase sequence obtained from the gene structure. K257 is the pyrid...

Pyridoxal phosphate-dependent histidine decarboxylase from Morganella morganii AM-15 was inactivated by (a-a-fluoromethylhistidine by a pseudo firstorder reaction, with KI and kinact values of 0 . 1 mM and 32.2 min-l, respectively, and was most efficient at pH 6.5-7.0. Both L-histidine and the competitive inhibitor, L-histidine methyl ester, protected against inactivation. The apoenzyme was not...

By kinetic studies and the identification of the labeled peptide of the [WIKNCO-modified protein, the inactivation of bovine liver glutamate dehydrogenase by potassium cyanate can be attributed to the carbamylation of the e-amino group of lysine-97. Although the e-amino group of lysine-97 is the major site of carbamylation by cyanate, the oc-amino group of alanine-l and E-amino group of lysine-...

We show that epd (gapB) mutants lacking an erythrose 4-phosphate (E4P) dehydrogenase are impaired for growth on some media and contain less pyridoxal 5'-phosphate (PLP) and pyridoxamine 5'-phosphate (PMP) than their epd+ parent. In contrast to a previous report, we found that gapA epd double mutants lacking the glyceraldehyde 3-phosphate and E4P dehydrogenases are auxotrophic for pyridoxine. Th...

2-Amino-3-ketobutyrate-CoA ligase (EC 2.3.1.29), or aminoacetone synthetase, has been purified by a nine-step procedure from 1.0 kg of beef liver to yield 8.8 mg of homogeneous enzyme. The homogeneous form of the enzyme, a monomer of M(r) = 44,000, shows unusually high absorption at 430 nm, with a ratio of absorbance at 280 and 430 nm of 2.6. On storage a species with an additional absorption p...

The three-dimensional structures of rabbit and human liver cytosolic serine hydroxymethyltransferase revealed that H231 interacts with the O3' of pyridoxal-5'-phosphate and other residues at the active site such as S203, K257, H357 and R402 (numbering as per the human enzyme). This and the conserved nature of H231 in all serine hydroxymethyltransferases highlights its importance in catalysis an...