FEMS Microbiology Letters 29 (1985) 99-104 99 Published by Elsevier FEM 02196 Control of benzylamine oxidase activity in Kluyveromycesfragilis grown on primary amines as nitrogen source (Induction; ammonium repression; catalase) Lesley A. Sherlock * and Peter J. Large ** Department of Biochemistry, Universityof Hull, Hull HU6 7RX, U.K. Received 13 May 1985 Accepted 4 June 1985 1. SUMMARY After growth on a mixture of ammonium and either methylamine or n-butylamine as nitrogen sources, benzylamine oxidase activity in yeasts from a number of different genera was found to be repressed to a lesser extent by ammonium than was methylamine oxidase. Catalase activity was better repressed by ammonium with methylamine as the nitrogen source than with n-butylamine. During growth of Kluyveromyces fragilis on equimolar mixtures of ammonium and an amine as nitrogen sources, benzylamine oxidase synthesis began during the period of exclusive growth on ammonium, and a period of simultaneous use of both nitrogen sources was observed just before the ammonium was exliausted. Addition of am- monium to cultures growing on n-butylamine as nitrogen source had no immediate repressive effect on benzylamine oxidase or catalase synthesis. However, growth on limiting ammonium in the absence of amines did give rise to low levels of amine oxidase and derepression of catalase activ- ity. It is concluded that benzylamine oxidase in yeasts is induced strongly by amines as well as * Formerly Lesley A. Heath. ** To whom correspondence should be addressed. being less strongly repressed by ammonium than methylamine oxidase. 2. INTRODUCTION Growth on primary amines as nitrogen source by yeasts involves their catabolism by pathways in which the first step is catalysed by an amine oxidase [1,2]. Experiments with methylamine and ethylamine as nitrogen sources in the yeasts Candida utilis and Hansenula polymorpha [3] and with dimethylamine and trimethylamine in C. boidinii [4] showed that the formation of methyl- amine oxidase [1,5,6] was repressed very strongly by ammonium ions along with catalase (EC 1.11.1.6) and NADP-dependent glutamate dehy- drogenase (EC 1.4.1.4) and that the synthesis of these enzymes did not require the presence of an amine in the growth medium, i.e. that their synthe- sis is under repressive rather than inductive con- trol. In the present paper we present evidence that in K. fragilis (which contains no methylamine oxidase [7]), the synthesis of benzylamine oxidase can be induced by the amine substrates in the presence of excess ammonium ions, and the repression by ammonium, although present, is less strong. The 0378-1097/85/$03.30 © 1985 Federation of European Microbiological Societies