PH-DEPENDENT ASSOCIATION OF CARBONIC-ANHYDRASE (CA) WITH GASTRIC LIGHT MICROSOMAL-MEMBRANES ISOLATED FROM BOVINE ABOMASUM - PARTIAL CHARACTERIZATION OF MEMBRANE-ASSOCIATED ACTIVITY

1. The effect of pH on the association of carbonic anhydrase (CA) with bovine gastric light microsomal membranes (LMMs) was investigated (a) by washing LMMs containing CA activity with solutions of different pH s; (b) by studying the adsorption at various pHs of soluble bovine ery throcyte CA to washed gastric LMMs. In both cases, the association of CA with gastric LMMs was dependent on pH, being lower at neutral or al kaline pH. 2. The amount of soluble CA associated with gastric LMMs at pHs 8.0 and 9.0 was reduced when 140 mM K+/10 mM Na+ was added to the incubation medium. 3. Two sources of CA activity in bovine gastric LM Ms were assumed: a loosely- and a firmly-membrane-associated activity. Both CA activities were dose-dependently inhibited by acetazolamide ( I50: 3.6 x 10(-9) and 8.4 x 10(-9) M, respectively) and by chloride, a cetate, iodide, bromide and nitrate at 100 mM. Firmly-membrane-associa ted activity appeared to be less sensitive to inhibition by acetazolam ide, chloride and iodide. 4. Both activities exhibited different behav ior and stability following treatment with alkaline Triton X-100. 5. T he possible importance of a membrane-associated CA actyvity in gastric LMMs related to gastric acid secretion is discussed.