The carp M1 muscle‐specific creatine kinase subisoform is adaptive to the synchronized changes in body temperature and intracellular pH that occur in the common carp Cyprinus carpio

The three previously cloned Cyprinus carpio muscle‐specific subisoforms of creatine kinase (CK, EC 2.7.3.2) designated M1‐, M2‐ and M3‐CK were examined. At temperatures <15° C and at pH >7·7, specific activities of M1‐CK were three to eight‐fold higher than specific activities of M3‐ and rabbit (R) M‐CK. At pH 8·0, M1‐CK exhibited its highest specific activity at 15° C. Michaelis constants of PCr () and ADP () of M1‐CK were relatively stable at pH between 7·1–8·0 and 25–5° C. Its calculated activation energy of catalysis (E_a) at pH 8·0 was lower than at pH 7·1. Circular dichroism spectroscopy results showed that changes in secondary structures in M1‐CK at the pH and temperatures studied were much less than in the cases of RM‐ and M3‐CK. The M1‐CK enzyme seemed to have evolved to adapt to the synchronized changes in body temperature and intracellular pH of C. carpio.