Two different B-type creatine kinase subunits dimerize in a tissue-specific manner

Brain-type creatine kinase B-CK (EC 2.7.3.2) was purified from several chicken tissues, e.g. cardiac muscle, brain, gizzard and retina. Two major monomeric chicken B-CK subunits, designated Bb (basic) and Ba (acidic), which differ in isoelectric point, were separated by chromatofocusing in the presence of 8 M urea on a MonoP column. The two subunits were shown by peptide mapping, amino acid analysis and partial sequencing, as well as by immunological criteria, to be distinct B-CK polypeptides. The N-terminal sequence of 30 amino acid residues of Bb correspond entirely to data derived from a B-CK c-DNA clone termed H4 [(1986) Nucleic Acids Res. 14, 1449-1463], whereas the N-terminus of the acidic Ba species was blocked. Native dimeric B-CK isoenzymes obtained from these tissues were separated by ion exchange chromatography on a MonoQ column yielding two B-CK dimer populations, type-I and type-II B-CK, varying in relative proportions. Quantitation of the CK activity peak ratios of these two populations revealed the existence of a tissue-specific, post-translational mechanism regulating B-CK dimerization in neural tissues. Tissue-specific dimerization of the two distinct B-CK monomer species may represent a means of specifying the intracellular distribution of the dimeric B-CK subspecies.