Site‐directed mutagenesis of AMP‐binding residues in adenylate kinase Alteration of substrate specificity

Adenylate kinase is highly specific for AMP as phosphoryl acceptor. We have found that the replacement of Thr39 by Ala in the chicken muscle enzyme, alone or together with the replacement of Leu66 by Ile, caused remarkable increases in CMP and UMP activities with a concomitant decrease in AMP activity; therefore, the resulting mutant enzymes show CMP and UMP activities/AMP activity ratios much higher than the wild-type enzyme. The mutant enzyme in which Ala is substituted for Thr39 has a Vmax value for CMP comparable to that of CMP-UMP kinase.