Comparative Study on Denaturation of Carp and Alaska Pollack Myosin B Induced by Inorganic Pyrophosphate

Abstract

Effect of addition of inorganic pyrophoshate (PPi) along with MgCl₂ on denaturation of myosin B from Carp and Alaska pollack (pH 7.0) was studied.
When 1.0mM of PPi and of MgCl₂ was added to myosin B in a medium containing 0.5 M KCl and 40mM Tris-maleate (pH 7.0) and the mixture was stored at 10°C, the following changes were observed: (1) Viscosity together with ATP-sensitivity (%) of both myosin B decreased. (2) Ca-ATPase specific activity of carp myosin B was almost unchanged, while that of Alaska pollack myosin B was largely decreased. (3) The mode of thermal inactivation of carp myosin B Ca-ATPase changed from a slow single first order process to a biphasic first order process, while that of Alaska pollack myosin B Ca-ATPase remained a slow first order process. (4) The amount of actin together with tropomyosin released into 50mM KCl solution (pH 7.0) from Alaska pollack myosin B was larger than that from carp myosin B.
These results indicated that a considerable part of both carp and Alaska pollack myosin B was dissociated into actin and myosin upon mixing and storage with PPi-MgCl₂, and that the actin released from carp myosin B denatured preferentially, leaving the myosin in a free form, while the actin along with myosin released from Alaska pollack myosin B immediately denatured.