HETEROGENEITY OF SMOOTH-MUSCLE MYOSIN LIGHT-CHAIN KINASE CHARACTERIZATION OF ISOELECTRIC VARIANTS

Purified chicken gizzard myosin light chain kinase (MLCK) analyzed by anion-exchange high-performance liquid chromatography (HPLC) can be co nsistently resolved into three well separated peaks, termed alpha, bet a, gamma. These peaks are shown to correspond to differently charged f orms of MLCK with the charge difference between alpha, and beta twice as large as between beta and gamma. The isoelectric point and elution position of the peaks as well as their amplitudes are modified by phos phorylation or by autophosphorylation of MLCK suggesting that the obse rved charge differences are related to their different phosphate conte nt. The three forms appear to have similar apparent affinity for both the substrates, ATP and the isolated regulatory light chain, but their specific activities are different.