ALTERATION IN RELATIVE ACTIVITIES OF PHENYLALANINE DEHYDROGENASE TOWARDS DIFFERENT SUBSTRATES BY SITE-DIRECTED MUTAGENESIS

Glycine-124 and leucine-307 of phenylalanine dehydrogenase from Bacill us sphaericus were altered by site-specific mutagenesis to the corresp onding residues in leucine dehydrogenase: alanine and valine, respecti vely, These two residues have previously been implicated from molecula r modelling as important in determining the substrate discrimination o f the two enzymes, Single and double mutants displayed lower activitie s towards L-phenylalanine and enhanced activity towards almost all ali phatic amino acid substrates tested compared to the wild-type, thus co nfirming the predictions made from molecular modelling.