[Study of a protein complex from the brain which reduces actin viscosity. I. Composition and various properties of...

The method of isolation from bovine brain of a preparation containing 90 kDa- and 42 kDa-proteins is described. This preparation shortens actin filaments and therefore decreases viscosity of F-actin. The 42 kDa-component was identified as actin by one-dimensional peptide mapping. Quantitative densitometry has demonstrated that 90 kDa-protein and actin are present in the preparation in equimolar ratio. Fractionation of the preparation by gel-filtration, analytical centrifugation or electrophoresis under non-denaturing conditions showed that 90 kDa-protein and actin are in a light complex. This complex consists of one actin molecule and one molecule of 90 kDa-protein and has a sedimentation coefficient of 3.5S. Both beta- and gamma-isoelectric forms of actin are present in the complex.