STUDIES ON ADENOSINE TRIPHOSPHATE TRANSPHOSPHOORYLASES .8. HOMOGENEITY AND PHYSICOCHEMICAL PROPERTIES OF CRYSTALLINE ADENOSINE TRIPHOSPHATE-CREATINE TRANSPHOSPHORYLASE FROM CALF BRAIN

This crystalline protein has withstood several criteria of purity, e. g., sedimentation velocity, sedimentation equilibrium, liquid-boundary electrophoresis, electrophoresis on cellulose acetate, and polyacrylamide disc electrophoresis, provided certain “instability” problems are recognized. The molecular weight by sedimentation equilibrium and the value for [formula omitted] of the calf brain have been assigned; and apparently these values are only slightly higher than those reported for the rabbit muscle adenosine triphosphate-creatine transphosphorylase (Yue, R. H., Palmieri, R. H., Olson, O E., and Kuby, S. A. (1967b), Biochemistry 6, 3204). Similar to the rabbit muscle enzyme, the calf brain enzyme appears to consist of two noncovalently linked polypeptide chains; a conclusion deduced by sedimentation equilibrium studies conducted in 4 M guanidinum chloride, in the presence and absence of 2-mercapto- ethanol. Interestingly, the calculated frictional ratios appear to be identical for both calf brain and rabbit muscle enzymes, which might imply a similar over-all gross molecular shape, in solution. However, the electrophoretic mobilities (liquid boundary and on supporting media) have revealed large differences in the isoelectric points for the calf brain vs. calf muscle isoenzyme (pI0 = 5.6 vs. 7.3, at zero ionic strength), indicative of significant differences in their charge distributions. Coincident with the electrophoretic studies on the calf isoenzymes, the contrast between the more stable molecular unit to be found in the muscle enzyme vs. the brain enzyme has become evident. © 1968, American Chemical Society. All rights reserved.