Acetolactate synthase ofLeuconostoc lactisand its regulation of acetoin production

Abstract

Summary: The acetolactate synthase ofLeuconostoc lactisNCW1 was studied. The Mn²⁺content of cell free extracts was 3·2 µ/mg protein. The enzyme did not require Mn²⁺for activity, had an optimum pH between 5 and 6 and was labile. Incubation at 21 °C or addition of thiamine pyrophosphate followed by storage at 4 °C stabilized the enzyme. It was allosteric with at least two binding sites for pyruvate and was inhibited by several products of glucose metabolism (6-phosphogluconate, 3-phosphoglycerate, 2-phosphoglycerate, PEP and ATP) at pH 5·4. Except for ATP, which became more inhibitory, the inhibition disappeared completely (6-phosphogluconate, 2-phosphoglycerate, and PEP) or partly (3-phosphoglycerate) at pH 4·7. The role of these compounds in the regulation of acetoin production from citrate by leuconostocs is discussed.