Biopolymers and cell. 1995; 11 (2): 57 - 68

SUPRAMOLECULAR ORGANISATION AND ACTIVITY OF SMOOTH MUSCLE MYOSIN LIGHT CHAIN KINASE

A. M. Filenko, A. Sobieszek, E. B. Babiychuk, V. S. Omelyanuk, V. M. Danilova, N. B. Yanovskaya, A. Yu. Babenko

The data received by the use of lazer correlation spectroscopy (LCS) suggest that inactive MLCK under conditions close to the physiological exists as mixture of oligo-meric and dimeric particles with hydrodynamic diameters about 150 and 20 nm, respe¬ctively. These particles should be in dynamic equilibrium. We could not discover noti¬ceable alteration in different kinase species distribution at both kinase or calmodulin excess in solution. At considerable excess of kinase over calmodulin the activity of the former is decreased several times after 5 to 10 min from the moment of its activation. Observed kinase inhibition in the preincubation time (before addition of substrate) must be connected with slow conformational rearrangements of activated kinase molecules which is directly confirmed by the results of our fluorescent studies. Such conformational rearrangements accompanied by the reduction of MLCK towards CaM affinity take place also at equimolar ratios of kinase to CaM, but in this case they are characterised by the lesser depth and insignificant MLCK activity decrease. Slow conformation chan¬ges in supramolecular structures of activated kinase are believed to have collective cha¬racter and to be connected with intensification of mutual influence of kinase molecules leading to reduction of CaM binding.