Regulation of Tryptophan Biosynthesis in the n-Alkane Utilising Yeast Candida maltosa

Abstract

Summary The enzymes of tryptophan pathway were partially purified from Candida maltosa and the regulation patterns were established. Ammonia-dependent anthranilate synthase (ASN) (M r 40,000), anthranilate phosphoribosyltransferase (PRT) (M r 100,000), phosphoribosylanthranilate isomerase (PRAI) (M r 30,000), and tryptophan synthase (TS) (M r 140,000) are separated from each other, whereas glutamine-dependent anthranilate synthase (ASG) is active only in complex (M r 75,000) with indole-3-glycerol-phosphate synthase (InGPS). The formation of three enzymes (ASN, PRT, ASG-InGPS) was regulated by the general control of amino acid biosynthesis, whereas synthesis of PRAI and TS was constitutive. Tryptophan only affected both anthranilate synthase activities. The K m -values of ASN were 0.083 mi for chorismate and 10 mM for ammonium. Inhibition of the enzyme reaction by tryptophan was competitive with respect to chorismate (K i = 0.007 mM). The K m -values of ASG were estimated to be 0.043 mM for chorismate and 1.0 mM for glutamine; a K i of 0.004 mM was obtained for tryptophan. A number of tryptophan analogues also inhibited the two enzyme reactions.