Purification and characterization of cytoplasmic creatine kinase isozymes ofXenopus laevis

The soluble creatine kinase isozymes CK-II, CK-III, and CK-IV fromXenopus laevis have been purified to apparent homogeneity and their subunits characterized by means of molecular weight, peptide pattern, and dissociation-reassociation experiments. CK-III and CK-IV are homodimeric isozymes whose subunits are distinct in both molecular weight (42,000 and 41,000, respectively) andStaphylococcus aureus V8 peptide pattern. In dissociation-reassociation experiments, those two subunits do form active heterodimeric isozymes with one another or with rabbit M-CK subunits. Hybrid CK-III/IV isozymes occur also during embryonic differentiation and in adult heart muscle, whereas most other adult tissues contain only homodimeric CK-III or CK-IV isozymes. The CK-II isozyme is a heterodimer composed of one CK-III subunit and another subunit specific to CK-II (Mr=41,000). Neitherin vivo norin vitro does this subunit seem able to form homodimers or heterodimers with CK-IV and rabbit M-CK subunits. If we take into account the apparent association of CK-I isozyme with cellular organelles, these results corroborate earlier statements and suggest that the CK isozyme system ofX. laevis is encoded by at least four differentially regulated genomic loci.

来自非洲爪蟾的可溶性肌酸激酶同工酶CK - II、CK - III和CK - IV已被纯化至明显的均一性，并且通过分子量、肽谱以及解离 - 再结合实验对其亚基进行了表征。CK - III和CK - IV是同型二聚体同工酶，其亚基在分子量（分别为42,000和41,000）以及金黄色葡萄球菌V8肽谱方面均不同。在解离 - 再结合实验中，这两种亚基确实能彼此之间或与兔肌型肌酸激酶（M - CK）亚基形成有活性的异型二聚体同工酶。杂合的CK - III/IV同工酶也出现在胚胎分化过程中和成年心肌中，而大多数其他成年组织仅含有同型二聚体的CK - III或CK - IV同工酶。CK - II同工酶是一种异型二聚体，由一个CK - III亚基和另一个CK - II特异性亚基（分子量为41,000）组成。无论是在体内还是体外，该亚基似乎都不能与CK - IV和兔M - CK亚基形成同型二聚体或异型二聚体。如果我们考虑到CK - I同工酶与细胞器的明显关联，这些结果证实了早期的论断，并表明非洲爪蟾的肌酸激酶同工酶系统是由至少四个受不同调控的基因组位点编码的。