MEMBRANE-ASSOCIATED CARBONIC-ANHYDRASE OF PEA THYLAKOIDS

A method for isolation of pea thylakoids exhibiting carbonic anhydrase activity is described. It is shown that this activity is not due to c ontamination with soluble carbonic anhydrase (CA). The hydrase carboni c anhydrase activity of thylakoids increases on treatment with 0.01-1. 0 mu M azide or acetazolamide, whereas the activity of soluble CA decr eases. The dehydrase activity of membrane-associated CA of thylakoids (tCA) was measured at room temperature over a wide range of pH using a specially designed device. Treatment of the thylakoids with low conce ntrations of Triton X-100 in the presence of Delta pH on the membrane increased tCA activity when the pH of the medium was higher than the p H of the lumen, and to a decrease in its activity under the opposite c onditions. No differences were found in the activities of control and Triton-treated thylakoid preparations either in the absence of Delta p H or when the membranes were severely broken by high Triton X-100 conc entration. This finding suggests that the tCA activity is controlled b y the pH value near the stromal surface of the membrane. The results s uggest the presence of functionally active carbonic anhydrase in thyla koid membranes of C-3-plants.