Conversion of Pyruvate Under Natural and Artificial Anaerobiosis in Maize

Abstract

Lactate is formed during the initial hours of seed swelling during natural anaerobiosis in maize. Ethanol is formed later, at a concentration greater by one order. With 7-day-old seedlings, first lactate and then ethanol are also formed after transfer of the plants to an atmosphere of nitrogen. Lactate and alcohol dehydrogenases are active in the germinating seed.

The molecular weight of maize alcohol dehydrogenase (EC 1.1.1.1) is 62 000 ± 5000. Inhibition by chelating agents and 'sulphydryl poisons' indicates the probable presence of metal and -SH groups. The enzyme oxidizes ethanol at an optimum pH of 8.7 with a K_m of 1.8 x 10^-2 M and reduces acetaldehyde at an optimum pH of 6.7 with a K_m of 1.0 x 10^-3M. It is inhibited by succinate, malate, lactate and acetate, non-competitively with respect to the substrate. Acetoxime is a competitive inhibitor and butyrylamide, acetamide and cyclohexanone oxime are non-competitive inhibitors.