Bacterial origin of alkaline l-serine dehydratase in French beans

Abstract

Two l-serine dehydratases with pH optima at pH 5·5 and 9·0, respectively, have been identified in homogenates of French bean seedlings. The l-serine dehydratase activity with optimum at pH 9·0 increases as the plant extract ages and this correlates with bacterial growth in the extract; appearance of the enzyme in plant homogenates was retarded by the antibacterial agent, chloromycetin. The main bacteria associated with the plant extracts were identified as Erwinia herbicola and Pseudomonas fluorescens. Examination of cell free extracts of these bacteria show that the Pseudomonas fluorescens contains an active l-serine dehydratase. Whole cells of the bacterium show optimum activity towards l-serine at pH 9·0. It is concluded that in French bean homogenates this l-serine dehydratase may be of bacterial origin; in contrast, the enzyme with optimum at pH 5·5 appears to be a plant enzyme.