EFFECT OF TRANSMEMBRANE Ca2+ GRADIENT ON CONFORMATION AND ENZYME ACTIVITY OF RECONSTITUTED ADENYLATE CYCLASE

Adenylate cyclase from bovine brain cortex was reconstituted into asolectin liposomes with （500-fold） or without transmembrane Cagradient. The enzyme activity of four types of proteoliposomes （the active center of enzyme exposing outside） was compared. The highest adenylate cyclase activity was observed in the vesicles with outside lower Caconcentration (≈10mol/L, similar to thephysiological condition). If the transmembrane Cagradient was in the inverse direction (i.e. outside higher Caconcentration, 0.5 mmol/L), a lowest enzymatic activity would appear. The difference in enzymatic activity between the two types of proteoliposomes could be diminished following the addition of Caionophore A23187. Proteoliposomes without transmembrane Cagradient exhibited intermediate activities.The conformation difference of adenylatecyclases in the above-mentioned proteoliposomes was also detected by measuring intrinsic fluorescence and fluorescence quenching with KI.