A hydrophobic region on myosin light chains modulated by divalent cations

Abstract A hydrophobic region was detected on several types of myosin light chain by enhancement of the quantum yield of 1-anilino-8-napthalenesulfonate (ANS) fluorescence. The character of this non-polar region was altered by the binding of Ca 2+ or Mg 2+ to the light chain, the quantum yield of the ANS being increased, and its emission maximum undergoing a blue-shift. These changes enabled the binding of divalent cations to the myosin light chains to be monitored. When Ca 2+ was bound to gizzard regulatory light chain, a biphasic enhancement of light-chain-bound ANS fluorescence occurred, the first phase taking place in the micro-eolar range and the second in the millimolar range of free Ca 2+ concentration. Enhancement of protein-bound ANS fluorescence as divalent cations were bound was also observed with other types of myosin light chain.