Biosynthesis of cytochalasans. XI. New results on the incorporation of phenylalanine into cytochalasin D by Zygosporium masonii [1].

Incorporation of L-[2-2H]phenyl-[2-2H]alanine and L-phenyl-[2-13C, 15N]alanine into cytochalasin D by Zygosporium masonii involved the complete loss of both the alpha-2H- and the alpha-15N-atom. Incorporation of a mixture of L-phenyl-[15N]alanine and L-[U-14C]phenylalanine into cytochalasin D and protein amino acids (phenylalanine, leucine, isoleucine) was accompanied by a substantial loss of 15N with respect to 14C. These effects are attributed to rapid exchange reactions taking place while L-phenylalanine is part of the intracellular pool of amino acids. In addition, the medium- and concentration-dependent incorporation of the carbon skeleton of exogeneous D-phenylalanine into cytochalasin D is reported. In a peptone-based complex medium, D-phenyl-alanine is poorly incorporated. Throughout the whole concentration range (0-250 mg/l), the incorporation rates are less than 10% of those of L-phenylalanine. In a minimal medium containing NH4NO3 as nitrogen source however, D-phenylalanine is preferred over the natural enantiomer by a factor of 1.28 up to 6.78, depending on the concentrations of exogeneous D- and L-phenylalanine. These effects are attributed to the medium-dependent activities of different amino acid transport systems responsible for the uptake of D- and L-phenylalanine in Z. masonii.