The ε Subunit of the Chloroplast Coupling Factor 1 from Euglena gracilis

The coupling factor from chloroplasts (CF(1)) of Euglena gracilis Z strain is an active ATPase in situ, and its activity cannot be increased by treatment with trypsin or heating as is the case with the CF(1) from other sources. The smallest subunit of CF(1), the epsilon subunit, is supposed to be involved in controlling the ATPase activity. We have devised a simple technique for rapid and large-scale isolation of this subunit. The epsilon subunit from Euglena CF(1), although having only a limited inhibitory effect on Euglena CF(1), drastically inhibited the ATPase activity of heat-activated spinach CF(1). The inhibition of spinach CF(1) could be reversed by passage through Sephadex G-50 or by a second heat activation. An antibody to the epsilon subunit of Euglena CF(1) cross-reacted only weakly with CF(1) from spinach, Sorghum, Kalanchoë, or Anacystis nidulans, but reacted well with whole Euglena CF(1) in addition to its epsilon subunit. The antibody increased the ATPase activity of Euglena and Anacystis CF(1) and of unactivated or partially activated spinach CF(1). The results suggest that the function of the epsilon subunit in Euglena CF(1) is similar to its function in CF(1) from other sources. The data also suggest that changes induced in spinach CF(1) by activation involves modifications in subunits other than the epsilon one.