Induced fit in arginine kinase

Creatine kinase (CK) and arginine kinase (AK) are related-enzymes that reve rsibly transfer a phosphoryl group between a guanidino compound and ADP. In the buffering of ATP energy levels, they are central to energy metabolism and have,been paradigms of classical enzymology, Comparison of the open sub strate-free structure of CK and the closed substrate-bound structure of AK reveals differences that are consistent with prior biophysical evidence of substrate-induced conformational changes. Large and small domains undergo a hinged 13 degrees rotation. Several loops become ordered and adopt differe nt positions in the presence of substrate, including one (residues 309-319) that moves 15 Angstrom to fold over the substrates, The conformational cha nges appear to be necessary in aligning the two substrates for catalysis, i n configuring the active site only when productive phosphoryl transfer is p ossible, and excluding water from the active Site to avoid wasteful ATP hyd rolysis.