Purification and properties of leucine aminotransferase from soybean seedlings

Abstract

Two isoenzymes of leucine aminotransferase (LAT I and LAT II) were extracted and partially purified from etiolated soybean seedlings. LAT I accounted for about 87% and LAT II about 13% of the total LAT activity. LAT I was eluted from a DEAE-cellulose column with a buffer having lower ionic strength than LAT II. Both isoenzymes gave pH optima of 8.9. Kinetic data for the forward reaction were consistent with the accepted ping-pong bi-bi mechanism for aminotransferases. Isoenzymes were inhibited by excess of substrate and product. Inhibition by the substrate analogue maleate suggested that both substrates utilized the same catalytic site of the enzyme. Hydroxylamine inhibited the aldehyde form of the LAT while the amino form was found to be inert.