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B6db references: 14093919

type Journal Article
authors Dempsey WB, Snell EE
title Pyridoxamine-Pyruvate Transaminase. II. Characteristics of the Enzyme
journal Biochemistry
sel unselected
ui 14093919
year (1963)
volume 2
number 6
pages 1414-9
abstract Improved procedures are described for the purification and determination of pyridoxamine- pyruvate transaminase, which catalyzes the reversible reaction: pyridoxamine + pyruvate = pyridoxal + L-alanine The specific activity of the crystalline enzyme is substantially higher than previously reported. In addition to pyridoxamine, 5-deoxypyridoxamine and omega-methylpyridoxamine are excellent substrates in reaction (la); pyridoxamine-5-P undergoes slow reaction at high concentrations. Of nineteen amino acids tested, only alpha-aminobutyrate replaced alanine as substrate in reaction (lb). Pyridoxylalanine is a potent and specific inhibitor of the reaction; its affinity for the enzyme (KĄ = 1.8 X 10 -7 m) is far higher than that for either pyridoxal (Km = 1.5 X 10-5 m) or L-alanine (Km = 2 X 10-3 m). Pyridoxine and certain related compounds are much less effective inhibitors. One mole of pyridoxal, 5-deoxypyridoxal, or pyridoxal 5-phosphate binds per 60,000 g of enzyme. Reduction of the enzyme with sodium borohydride in the absence of pyridoxal does not inactivate it; in the presence of pyridoxal inactivation is proportional to the amount of pyridoxal bound and to the increase in absorbancy at 325 nm (pH 7.0). This absorption maximum is accounted for quantitatively by the formation of epsilon-pyridoxyllysine residues in the reduced protein. The findings show that a lysine residue is part of the active site of the enzyme. The crystalline enzyme contains no metal ions; its amino acid analysis shows it to be unusually rich in proline.
last changed 2017/12/14 11:26

B6db references