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B6db references: 85021429

type Journal Article
authors Shioi, Y.; Nagamine, M.; Sasa, T.
title Purification and properties of L-alanine:4,5-dioxovalerate aminotransferase from Chlorella regularis
journal Arch Biochem Biophys
ui 85021429
year (1984)
volume 234
number 1
pages 117-24.
keywords Catalysis
abstract The enzyme L-alanine:4,5-dioxovalerate aminotransferase (EC, which catalyzes the synthesis of 5-aminolevulinic acid, was purified 161-fold from Chlorella regularis. The enzyme also showed L- alanine:glyoxylate aminotransferase activity (EC The activity of glyoxylate aminotransferase was 56-fold greater than that of 4,5-dioxovalerate aminotransferase. The ratio of the two activities remained nearly constant during purification, and when the enzyme was subjected to a variety of treatments. 4,5-Dioxovalerate aminotransferase activity was competitively inhibited by glyoxylate, with a Ki value of 0.5 mM. Double-reciprocal plots of velocity versus 4,5-dioxovalerate with varying L-alanine concentrations indicate a ping- pong reaction mechanism. The apparent Km values for 4,5-dioxovalerate and L-alanine were 0.12 and 3.5 mM, respectively. The enzyme is an acidic protein having an isoelectric point of 4.8. The molecular weight of the enzyme was estimated to be 126,000, with two identical subunits. These results suggest that, in Chlorella, as in bovine liver mitochondria and Euglena, both 4,5-dioxovalerate and glyoxylate aminotransferase activities are associated with the same protein. From the activity ratio of transamination and catalytic properties, it is concluded that this enzyme does not function primarily as a part of the 5-carbon pathway to 5-aminolevulinic acid synthesis.
last changed 2002/11/12 16:17

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