[Conformational modifications of smooth muscle light chain kinase].

Our recent investigations have shown that smooth muscle myosin light chain kinase (MLCK) exists in solution as a mixture of oligomeric, dimeric and monomeric species; besides during preincubation (maintaining of the activated enzyme without substrate) with substoichiometric amounts of calmodulin (CaM) it undergoes definite changes leading to several fold lowering of its activity. Fluorescent data obtained in this work suggest that such kinase inhibition must not be connected with quantitative redistribution of different kinase species but rather it is the result of conformational modifications of this enzyme activated molecules leading to the reduction of their affinity to CaM. Such conformational rearrangements took place also at equimolar kinase to CaM ratio (or CaM excess) but in this case they were characterized by lower depth and insignificant MLCK activity fall. The nature of these conformational changes is discussed.