A hydrodynamic, enzymatic and CD spectroscopic study of skeletal muscle myosin light chain kinase, three proteolytic fragments and corresponding complexes with calmodulin was performed. A refined shape model was built for the enzyme. It was shown that a head-and-tail structure is formed from two major fragments which are aligned end-to-end. The one fragment (Mr 36000) is compact, of high alpha-helix content and contains the catalytic center with the light chain and the calmodulin binding domains. The other fragment (Mr 33000) with unknown function is asymmetric (a/b greater than 10), of low alpha-helix and of unusually high proline content.
