Some properties of calcium-activated adenosine triphosphatase from the hermatypic coral Galaxea fascicularis

Abstract

Samples of the hermatypic coral Galaxea fascicularis were collected between April 1987 and April 1990 from coral reefs off Singapore (103 °45′E; 1 °13′N). Ca2+-activated adenosine triphosphatase (ATPase) activity was detected in the plasma-membrane-enriched heavy microsomal fraction of G. fascicularis. The high affinity component had Km and Vmax values of 0.0021 m M and 0.050 μmol Pi mg-1 protein min-1, respectively; corresponding values for the low affinity component were 0.15 m M and 0.85 μmol mg-1 protein min-1. The activity of the high affinity component was inhibited 80 and 50%, respectively, by the anticalmodulin drugs calmidazolium and chlorpromazine. The low affinity component of the Ca2+-ATPase may represent activities of alkaline phosphatase, Ca2+-ATPase from membranes of mitochondria and endoplasmic reticulum, or calmodulin-dissociated plasma membrane Ca2+-ATPase resulting from the removal of Ca2+ by EDTA during the isolation process. The high affinity Ca2+-ATPase is probably the enzyme responsible for Ca2+ extrusion from the cells of G. fascicularis. The high and low affinity components of this Ca2+-ATPase could use ATP and ADP as substrates. Maximum activities of both components were registered at pH 7 and at 45°C. Ruthenium red, a specific inhibitor of Ca2+-ATPase, inhibited the activities of the high and low affinity Ca2+-ATPase by 100 and 60%, respectively. Inhibition of the activities of both components was also observed with sulphydryl reagents (PCMB and mersalyl). However, DCMU, diamox, dinitrophenol, iodoacetate, fluoride, cyanide, ouabain, oligomycin B and L-phenylalanine had no effect on the enzyme activities. © 1991 Springer-Verlag.