Substrate-binding and catalytic roles of Lys194 in the C-terminus in human adenylate kinase by site-directed random mutagenesis.

Site-directed random mutagenesis of Lys194 residue in the C-terminus of human adenylate kinase (AK) was performed, and six mutants were analyzed by steady-state kinetics. K194-mutants variously affected the apparent Michaelis constants (K(m) values) for ATP and AMP, although the kcat values strikingly decreased. The Lys194 residue appears to interact not only with MgATP2- but also with the AMP2- substrates by salt bridge formation with a nucleotide and to play a functional role in stabilizing the phosphate-transfer during catalysis. Lys194 could be essential for substrate-holdings and in catalysis and not replaceable to the other amino acids.