Receptor‐binding capability of pancreatic phospholipase A2 is separable from its enzymatic activity

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Abstract
Mammalian pancreatic phospholipase A2 (PLA2‐I) has its specific receptor through which PLA2‐I induces a variety of biological responses. In this study, a fundamental relationship between the enzymatic and the receptor‐binding activities of PLA2‐I was investigated. The specific binding of PLA2‐I to the receptor was found to be independent of Ca2+ which is requisite for the PLA2 activity. On the basis of this observation, we designed and produced mutant PLA2‐Is without Ca2+‐binding abilities in order to demonstrate that the structural requirement for the enzymatic activity of PLA2‐I is not identical with that for its receptor‐binding reaction. These mutant PLA2‐Is lost almost all enzymatic activity through a disturbance at the Ca2+‐binding site, as expected, but still retained a substantial affinity to the receptor, allowing us to conclude that the receptor‐binding reaction of PLA2‐I is separable from its catalytic action.