STRUCTURE AND FUNCTION OF CHLOROPLAST PROTEINS .9. FURTHER COMPARATIVE STUDIES ON CHLORELLA AND SPINACH LEAF RIBULOSE-1,5-DIPHOSPHATE CARBOXYLASE

A highly purified preparation of ribulose-1,5-diphosphate carboxylase was obtained from autotrophically grown cells of Chlorella ellipsoidea. The molecular dimension of the enzyme was similar to that isolated from spinach leaf; S20,w value of 18.4 and a cubical oligomeric structure of the protein molecule (d = ca 100 μ) as revealed by an electron microscope. Amino acid composition of the algal carboxylase was found to be similar to that of the spinach carboxylase. However, from both the quantitative immunochemical precipitin test and the enzyme-inhibition experiment using the rabbit anti-spinach RuDP carboxylase serum, there was found to exist am immunological difference between spinach and Chlorella RuDP carboxylases. The subfragment formed from the Chlorella enzyme protein by 4.0 m urea did not retain the carboxylase activity, although the spinach enzyme was split into an enzymically active subfragment under the same treatment. © 1969.