STUDIES ON CARBONIC-ANHYDRASE (CA) OF LIGHT MICROSOMAL-MEMBRANES ISOLATED FROM BOVINE AND PIG GASTRIC-MUCOSA

1. The occurrence and characteristics of carbonic anhydrase (CA) activ ity were studied in light microsomal membranes (LMM) purified from bov ine gastric mucosa. 2. Bovine gastric LMM contained a high activity of CA ranging from 170 to 400 mu mol.H + /min/mg protein when assayed at 0-degrees-C by pH-stat technique. 3. The addition of 2 mM EDTA to the assay mixture increased the enzyme activity. Lower concentrations (0. 5-1 mM) had no effect. 4. The enzyme activity was dose-dependently inh ibited by acetazolamide and furosemide (I50:5 x 10(-10) M and 4.8 x 10 (-7) M, respectively) and by chloride ion (K(i) 85 mM) and appeared to be quite stable to treatment with alkaline Triton X-100. 5. Most of t he CA activity is loosely associated with the LMM since it was removed by different washing treatments. Nevertheless, after extensive washes , gastric LMM still contained CA activity suggesting the existence of a firmly membrane-associated form of CA. 6. Values of CA activity high er than those reported previously were found in pig gastric LMM. Furth ermore, the washing treatments described in this work were more effect ive in washing CA activity off pig gastric LMM than procedures describ ed previously.