Effects of substrate structural analogues on the enzymatic activities of aspartate aminotransferase isoenzymes.
Aspartate aminotransferase (AAT, EC 2.6.1.1) catalyses the transamination of L-asparate to oxaloacetate. It has been reported that AAT from different plant sources can catalyse the transamination of other compounds structurally similar to the natural substrates. Specificity and kinetic studies were performed with two aspartate aminotransferase isoenzymes (AAT-1 and AAT-2) from leaves of Lupinus albus L. cv Estoril using different amino donors and acceptors. Both isoenzymes showed residual activity for some of the substrates tested. Competitive inhibition was found with most of the structural analogues which is typical of a ping-pong bi-bi kinetic mechanism. It was found that both isoenzymes can use 2-amino-4-methoxy-4-oxobutanoic acid as amino donor. AAT-2 uses 2-amino-4-methoxy-4-oxobutanoic acid at a similar rate as L-aspartate but AAT-1 uses this substrate at a slower rate. The use of this amino donor by AAT isoenzymes has not been reported previously, and our results indicate structural differences between both isoenzymes.
Martins
L L
LL
Instituto Superior de Agronomia-Departamento de Química Agrícola e Ambiental, Tapada da Ajuda, 1349-017 Lisboa, Portugal. luisalouro@isa.utl.pt
Mourato
M P
MP
de Varennes
A
A
D000596:Amino Acids / Q000737:chemistry / Q000378:metabolism; D001219:Aspartate Aminotransferases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D002087:Butyrates / Q000737:chemistry / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism / Q000494:pharmacology; D007887:Fabaceae / Q000201:enzymology*; D007527:Isoenzymes / Q000302:isolation & purification / Q000378:metabolism*; D007656:Ketoglutaric Acids / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology; D010940:Plant Proteins / Q000378:metabolism; D013379:Substrate Specificity
D000596:Amino Acids; D002087:Butyrates; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D007656:Ketoglutaric Acids; D010940:Plant Proteins; D001219:Aspartate Aminotransferases