돼지 심장 근육에서 추출된 mitochondrial creatine kinase의 반응 특성과 cytoplasmic creatine kinase의 반응 특성을 비교 연구하였다. Mitochondrial creatine kinase의 최적 반응 pH는 정반응뿐만 아니라 역반응에 있어서도 cytoplasmic creatine kinase 것보다 다소, 낮았고, 또한 pH 7.0과 8.0 사이에서 mitochondrial creatine kinase의 정반응과 역반응의 최고 속도비는 cytoplasmic creatine kinase의 것보다 월등히 높음을 관찰하였다. 기질들에 대한 효소의 친화도는 mitochondrial creatine kinase가 cytoplasmic creatine kinase 것보다 2배 정도 강함을 알 수 있었다. 더우기 pH 7.4에서 반응 평형 상수 ($K_{eq}$)는 mitochondrial creatine kinase의 경우 $1.48{ imes}10^{-2}$, cytoplasmic creatine kinase의 경우 $7.20{ imes}10^{-3}$ 임을 보였고 이 결과는 mitochondrial creatine kinase는 cytoplasmic creatine kinase 것보다 정반응쪽 반응이 2배 정도 유리함을 시사해 준다. 이 외에도 mitochondrial creatine kinase의 초기 속도 반응 및 product 저해 작용의 반응 형상들은 cytoplasmic creatine kinase 것과 유사함을 보였고, 이 결과로부터 두 반응 경우 모두 rapid equilibrium, random 유형의 반응 기작을 따름을 알 수 있었다. 이상의 실험 결과를 바탕으로 mitochondrial creatine kinase의 생화학적 역할을 추측하고자 하였다.
The mitochondrial creatine kinase was isolated from pig heart muscle, and its kinetic properties were compared with those of cytoplasmic isoenzyme. The optimum pH for both forward and reverse reaction of mitochondrial enzyme was observed to be slightly lower than that of cytoplasmic enzyme. Also it was found that at the pH between 7.0 and 8.0 the ratio of maximal forward to reverse reaction of mitochondrial enzyme is higher than that of cytoplasmic isoenzyme. The affinities of mitochondrial enzyme toward its substrates were estimated to be stronger than those of cytoplasmic enzyme at the through-out pH studied. The over-all equilibrium constant($K_{eq}$) at pH 7.4 was estimated to be $1.48{ imes}10^{-2}$ and $7.20{ imes}10^{-3}$ for the mitochondrial and the cytoplasmic isoenzymes, respectively. The characteristic patterns of the initial velocities and the product inhibitions for the mitochondrial creatine kinase forward reaction at pH 7.4 was appeared to be same as those of cytoplasmic creatine kinase reaction exept that for mitochondrial reaction there is a marked inhibition of the maximal velocity against the increasing concentration of phosphocreatine. Based on the results of a series of comparative kinetic studies, we will discuss the physiological role of heart mitochondrial creatine kinase in the energy metabolism of the heart muscle system.
