A potent inhibitory protein of chloroplast or mitochondrial ATPase found in aprotinin preparation

1. Introduction During the course of investigations of the mechanism of energy-transducing system in living cells, various ATPase inhibitors have been found in the ATPase molecule; chloroplast ATPase inhibitor (CFi-I) [l], mitochondrial ATPase inhibitor (Fi-I) [2], bacterial ATPase inhibitor (BFi-I) [3] and one of the troponin components in muscle (TN-I) [4]. They were found as one component of the subunits in each ATPase molecule and play an important role in regulating the ATPase activity. It has been shown in our laboratory that a troponin component, TN-I, inhibits non-competitively mitochondrial, chloroplast or bacterial ATPase, and that the Fi -inhibitor inhibits strongly actomyosin or chloroplast ATPase [5-91. These experiments deal with the isolation of a protein from a commercial aprotinin preparation, which dramatically inhibits chloroplast and mito- chondrial ATPase. 2. Materials and methods An aprotinin preparation, Trasylol (lot no. 43 13p, 500 000 KIE/70-100 mg) [lO,ll], was supplied from Bayer AC. The chloroplast coupling factor 1 (CF,) was prepared from spinach by the method in [ 121 and was activated by heat at 60°C for 4 min. The mitochondrial coupling factor l(F i), AS-particles, was