Purification and characterization of 33 kilodalton protein of spinach chloroplasts

A protein was prepared from spinach chloroplasts in a highly purified form. The isoelectric point of the protein was 5.2. The apparent molecular weight was estimated to be 33 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and urea, and 34 000 by gel filtration column chromatography with Sephadex G-100. The protein was provisionally named '33 kilodalton protein' according to the molecular weight. The absorption spectrum of the protein did not show any absorption band in the visible region. No histidine was found in the amino acid analysis of the protein. The 33 kilodalton protein was released from the thylakoid membrane by EDTA-treatment and also by sonic oscillation. The protein was bound to System II particles, but not to System I particles.