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 pHs; (b) by studying the adsorption at various pHs of soluble bovine erythrocyte CA to washed gastric LMMs. In both cases, the association of CA with gastric LMMs was dependent on pH, being lower at neutral or alkaline 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 LMMs 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, acetate, iodide, bromide and nitrate at 100 mM. Firmly-membrane-associated activity appeared to be less sensitive to inhibition by acetazolamide, chloride and iodide. 4. Both activities exhibited different behavior and stability following treatment with alkaline Triton X-100. 5. The possible importance of a membrane-associated CA activity in gastric LMMs related to gastric acid secretion is discussed.
Departamento de Biologia, Facultad de Ciencias Exactas y Naturales, UNMDP, Mar del Plata, Argentina.
A A
AA
López Mañanes
G R
GR
Daleo
F V
FV
Vega
D000018:Abomasum / Q000201:enzymology* / Q000648:ultrastructure; D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D005753:Gastric Mucosa / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000201:enzymology; D008297:Male; D008861:Microsomes / Q000201:enzymology / Q000648:ultrastructure; D017830:Octoxynol; D011092:Polyethylene Glycols / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology
D002257:Carbonic Anhydrase Inhibitors; D011092:Polyethylene Glycols; D017830:Octoxynol; D012964:Sodium; D002256:Carbonic Anhydrases; D000086:Acetazolamide; D011188:Potassium