PURIFICATION AND CHARACTERIZATION OF EUKARYOTIC ALANINE RACEMASE ACTING AS KEY ENZYME IN CYCLOSPORINE BIOSYNTHESIS

A specific alanine racemase, which is a key enzyme in the biosynthesis of the undecapeptide cyclosporin A, was purified to electrophoretic homogeneity from the fungus Tolypocladium niveum. This is the first enzyme of this kind isolated from a eucaryotic organism. The enzyme catalyzes the reversible racemization of alanine and requires pyridoxal phosphate as the exclusive cofactor. K-m values for L- and D-alanine were found to be 38 and 2 mM, respectively. Maximal reaction velocity was observed at 42 degrees C and pH 8.8 for the L to D direction. Molecular mass determinations of the denatured enzyme by SDS-polyacrylamide gel electrophoresis gave a value of 37 kDa, whereas gel filtration calibration studies yielded a value between 120 and 150 kDa, indicating an oligomeric native structure.