Tryptophansynthase in Phycomyces blakesleeanus Teil I: Eigenschaften des Enzyms

Tryptophan synthase in Phycomyces blakesleeanus. Part I: Characterization of the enzyme. Tryptophan synthase was tested in light grown 5 days old cultures of Phycomyces blakesleeanus. The test was carried out only by reaction 3 (indole + serine → tryptophan + water) of the tryptophan synthase. The Km values for the substrates indole and serine were found to be 1.3 × 10‐4M and 1.0 × 10‐2M. Two Km values (1.5 × 10‐8M and 1.0 × 10‐6M) for pyridoxal 5′‐phosphate could be calculated from a Lineweaver‐Burk plot. The transformation of the Lineweaver‐Burk plot into the Hill plot resulted in a straight line with a rise of 0.35 for pyridoxal 5′‐phosphate. At higher concentrations the end product tryptophan and indole‐3‐acetic acid inhibit the tryptophan synthase in vitro.