Soluble Ca²⁺-Activated ATPase and Its Possible Role in Calcification of the CoccolithophoridCricosphaera roscoffensisvar.haptonemofera(Haptophyta) (Studies on the Calcium Carbonate Deposition of Algae V)

Abstract

Soluble Ca 2+ -activated ATPase was extracted from the calcareous alga Cricosphaera roscoffensis var. haptonemofera, and purified approximately 20-fold by DEAE-cellulose chromatography. The ATPase was characterized äs follows.The enzyme is activated by several divalent cations such äs Ca 2+ , Mg 2+ , Mn 2+ and Co 2+ , the most effective being Ca 2+ . Sr 2+ , Ba 2+ and La 3+ do not activate the enzyme. In the presence of 3 mM ATP, maximal enzyme activity is obtained at approximately 9 mM Ca 2+ . At the optimal Ca 2+ concentration, addition of Mg 2+ or La 3+ gives a strong inhibitory effect. Enzyme activation by Ca 2+ is not affected by Na + or K + .The optimal pH for Ca 2+ activation of the enzyme is approximately 9.6.The enzyme hydrolyzes several nucleoside tri-and diphosphates, but ATP serves äs the best Substrate with an apparent Km of 0.7 mM. /3-Glycerophosphate and p-nitrophenylphosphate are hardly hydrolyzed. The enzyme is inhibited by EDTA, ethacrynic acid, 7V-ethylmaleimide andp-CMB, but not by ouabain, Oligomycin, 2,4-dinitrophenol and DCCD. The enzyme is very unstable at 4 °C, but glycerol partially prevents inactivation of the enzyme.Noticeable activity of Ca 2+ -activated ATPase is also observed in the microsomal fraction.

V‐ AND P‐TYPE Ca2+‐STIMULATED ATPases IN A CALCIFYING STRAIN OF PLEUROCHRYSIS SP. (HAPTOPHYCEAE)

“…This compares to our findings on coccolithophorid Ca 2ϩ -stimulated ATPase in the coccolith vesicles, which did not require (in fact, it is inhibited by) Mg 2ϩ . The Ca 2ϩ -stimulated ATPase reported by Okazaki et al (1984) in C. roscoffensis and by Kwan and Kostka (1984) in animal cell membranes was also inhibited by Mg 2ϩ .…”

“…This report presents the first evidence demonstrating P-and V-type Ca 2ϩ -stimulated ATPases in the coccolithophorid algae. Although a soluble (not membrane bound) Ca 2ϩ -stimulated ATPase has been previously reported in the coccolithophore Cricosphaera roscoffensis, it was not characterized further (Okazaki et al 1984).…”

“…For organisms that also use HCO as a photosyn-Ϫ 3 thetic source of CO 2 within the plastid (those that have carbonic anhydrase in the chloroplast), the 1: 1 stoichiometric relationship between photosynthesis and calcification that has been generally observed among most of the calcifying algae has suggested that calcification has adaptive significance as a cytosolic pH-stat (McConnaughey 1991, Quiroga and González 1993, Israel and González 1996. Okazaki et al (1984) first reported Ca 2ϩ -stimulated ATPase in a coccolithophorid (Cricosphaera roscoffensis) cell extract. We later showed that Ca 2ϩ -stimulated ATPase was present at high levels in a calcifying strain of Pleurochrysis and distributed among all the major membranous fractions (Wainwright et al 1992, Kwon andGonzález 1994).…”

Calcium-Proton Exchange During Algal Calcification

“…1980). Ca 2+ and carbon presumably traverse the cytoplasm to reach the vesicular site of calcification, and Ca 2+ ATPase seems to be involved (Klaveness, 1976;Okazaki et al, 1984). Third, molecular CO 2 apparently provides most of the precipitating carbon during calcification by various plants and animals (McConnaughey, I989a, b, c), including Chara (Mc-Connaughey, in prep).…”

Rhodolith Physiology Across the Atlantic: Towards a Better Mechanistic Understanding of Intra- and Interspecific Differences

“…Generally, it is assumed that Cainflux to cells occurs through voltage sensitive Ca-channels, while Ca-efflux is associated to a Ca-ATPase (McConnaughey, 1989). The latter has been shown to be associated with calcification in corals and algae (e.g., Okazaki, 1977;Okazaki et al, 1984;Kingsley and Watabe, 1985). The "trans" calcification mechanism model proposed for these calcifiers suggests that Ca-ATPase supplies Ca 2+ to and removes H + from the site of calcification, resulting in an increase in pH and [Ca 2+ ] that FIGURE 8 | Summarized overview of the importance of CA ext and specific ion-transporters for rhodolith photosynthesis and/or calcification, based on inhibitor effects and accounting for declines in calcification caused indirectly by inhibitor effects on photosynthesis ("Both"-inhibitor effect on both processes, but larger in calcification, indicating direct effect on the latter; Supplementary Tables S3-S5).…”