Creatine kinase activity in the Torpedo electrocyte and in the nonreceptor, peripheral v proteins from acetylcholine receptor-rich membranes.

Publisher Website
Google Scholar
Abstract
The nonreceptor, peripheral .nu. proteins (MW 43,000 proteins) are conspicuous components of the acetylcholine receptor-rich membranes and the Torpedo electrocyte, so far devoid of any known enzymatic function. Creatine kinase (adenosine 5''-triphosphate:creatine N-phosphotransferase, EC 2.7.3.2) is identified in distinct polypeptides belonging to the family of .nu. proteins. Embryonic (70-90 mm embryos), neonatal and adult electric organs of T. marmorata contain 2 isoenzymes of creatine kinase: the BB (brain) and the MM (muscle) forms. The proportion of the 2 isoenzymes does not appear to change in the course of ontogenic and postnatal development. Only the BB isoenzyme appears to be associated with the acetylcholine-rich membranes in adult Torpedo. The creatine kinase can be purified to homogeneity by chromatographic procedures that exploit the richness in free sulfhydryl groups of the enzyme. Specific activities of 150 units/mg are obtained from electric tissue. The enzyme subunits identified by 2-dimensional gel electrophoresis and immunoblotting techniques have pI [isoelectric point] values in the 6.0-6.5 region and apparent MW in the 40,000-43,000 range, the latter values depending on redox conditions. [This study has implications for human muscular dystrophy.].