Light Chains of Abalone Myosin. UV Absorption Difference Spectrum and Resensitization of Desensitized Scallop Myosin

1. Abalone myosin consisted of one kind of heavy chain and two kinds of light chain according to SDS gel electrophoresis. The molecular weights of the light chains were estimated as 16,600 daltons (Light Chain-1: LC-1) and 14,500 daltons (Light Chain-2: LC-2). 2. The amino acid composition of LC-2 was not appreciably different from that of LC-1 except that the valine residue was 1 mol per mol of LC-2. 3. both LC-1 and LC-2 showed a calcium-induced UV absorption difference spectrum through the apparent binding constants for Ca2+ were low (2.5 x 10(-3) M for LC-1 and 3.2 x 10(-4) M for LC-2). 4. The modification of carboxyl groups of LC-2 by 1-ethyl-3(3-dimethylaminopropyl)carbodiimide caused the disappearance of the calcium-induced UV absorption difference spectrum. 5. Manganese ion could also induce a UV absorption difference spectrum with these light chains although the concentration of Mn2+ required to produce the difference spectrum was very high. 6. Abalone LC-2 bound to desensitized scallop myosin and restored the calcium sensitivity of the myosin but LC-1 did not.