Sharma R K, Kalra J
Department of Pathology, Royal University Hospital, University of Saskatchewan, Saskatoon, Canada.
Biochem J. 1994 Apr 1;299 ( Pt 1)(Pt 1):97-100. doi: 10.1042/bj2990097.
Calmodulin-dependent phosphodiesterase (CaMPDE) is one of the key enzymes involved in the complex interactions which occur between the cyclic-nucleotide and Ca2+ second-messenger systems. Calmodulin-dependent phosphodiesterase exists in different isoenzymic forms, which exhibit distinct molecular and/or catalytic properties. The kinetic properties suggest that the 63 kDa brain isoenzyme is distinct from the brain 60 kDa and heart and lung CaMPDE isoenzymes. The CaMPDE isoenzymes of 60 kDa from brain, heart and lung are regulated by calmodulin, but the affinities for calmodulin are different. At identical concentrations of calmodulin, the bovine heart CaMPDE isoenzyme is stimulated at a much lower Ca2+ concentration than the bovine brain or lung isoenzymes. The bovine lung CaMPDE isoenzyme contains calmodulin as a tightly bound subunit, so that a change in calmodulin concentration had no effect on the [Ca2+]-dependence of activation of this isoenzyme. These observations are consistent with the notion that differential regulation by calmodulin and Ca2+ is an important function of these isoenzymes, which provide fine-tuning mechanisms for calmodulin action.
钙调蛋白依赖性磷酸二酯酶（CaMPDE）是环核苷酸和Ca2+第二信使系统之间复杂相互作用中涉及的关键酶之一。钙调蛋白依赖性磷酸二酯酶以不同的同工酶形式存在，这些同工酶表现出不同的分子和/或催化特性。动力学特性表明，63 kDa的脑同工酶与脑60 kDa以及心脏和肺的CaMPDE同工酶不同。来自脑、心脏和肺的60 kDa的CaMPDE同工酶受钙调蛋白调节，但对钙调蛋白的亲和力不同。在相同浓度的钙调蛋白下，牛心脏CaMPDE同工酶在比牛脑或肺同工酶低得多的Ca2+浓度下受到刺激。牛肺CaMPDE同工酶含有紧密结合的钙调蛋白亚基，因此钙调蛋白浓度的变化对该同工酶激活的[Ca2+]依赖性没有影响。这些观察结果与以下观点一致，即钙调蛋白和Ca2+的差异调节是这些同工酶的重要功能，它们为钙调蛋白的作用提供了微调机制。
