| dc.description |
F-Actin (FA) and pyruvate kinase (PK) [EC 2.7.1.40] were immobilized on PAB-cellulose. HMM-Subfragment-1 (S-1) was applied to a column of immobilized FA and PK, and eluted with 1–1.5 μm ATP and 1 mM PEP in 50 mM KC1, 2 mM MgCl<sub>2</sub>, and 10 mM Tris-HCl at pH 7.8 and 4°. The size of the initial burst of P<sub>1</sub> liberation of S-1 applied to the column was 0.5 mole/mole. The size of the initial burst of S-1 in early fractions from the column was 0.8–0.9 mole/mole S-1. The burst size of S-1 decreased with increase in the fraction number, and S-1 in later fractions showed a burst size of 0.1–0.3 mole/mole. On the other hand, the rate of the ATPase [EC 3.6.1.3] reaction in the steady state was almost independent of the burst size, and increased slightly with increase in the fraction number.The ATPase activity of S-1 with a burst size of less than 0.2 mole/mole was scarcely activated by FA. Usually, the dependence on the burst size of S-1 of its ATPase activity in the presence of FA was sigmoidal, and marked activation by FA was observed when the burst size was larger than 0.3–0.4 mole/mole. Similar results were obtained with S-1 fractions separated by the ultracentrifugation method described in our previous paper ((1976) J. Biochem. 79, 419–434). |
