MOLECULAR ASPECTS OF ACTIVATION MECHANISMS OF CF1

The Ca2+-dependent ATPase activity of spinach chloroplast coupling fac tor 1 (CF1) is activated by treatment with dithiothreitol (DDT). If ex cess of this reagent is eliminated by gel filtration, an Eadie-Hofstee biphasic plot is obtained. These results are consistent with the exis tence of two active forms of the enzyme governed by the redox state. W e have observed that SDS-polyacrylamide gel electrophoresis pattern is affected by the pretreatment of the samples under those two different conditions. Spontaneous activation of the samples, due to a limited p roteolytic process, has also been detected. In this case the electroph oretic pattern was also affected. The protease implied in this process could be a cysteine protease co-isolated with CF1. These observations suggest that limited proteolysis, as well as redox-induced changes, a re involved in the physiological regulation of the enzyme.