CYANOGEN-BROMIDE FRAGMENTS OF THE LARGE SUBUNIT OF RIBULOSEBISPHOSPHATE CARBOXYLASE FROM BARLEY

The large subunit of ribulosebisphosphate carboxylase from barley has been subjected to cleavage with cyanogen bromide. The presence of 9 methionines among the about 490 amino acids in the polypeptide chain is expected to yield 10 fragments. Nine fragments have been identified and a tenth fragment was indicated in one cleavage experiment. Six cleavage products have been purified by gel filtration on Bio-Gel P-30 and ion-exchange chromatography on carboxymethyl-cellulose and sulphopropyl-Sephadex. They have been characterized by amino acid composition, N-terminal amino acid and tryptic peptide analysis. The N-terminal amino acid and the approximate molecular weight of these six fragments are: Ala, 15,000 dalton; Pro, 10,000 dalton; PyrGlu, 7,000 dalton; Ser, 6,000 dalton; Ile, 3,000 dalton; Pro, 2,000 dalton. Two fragments (Arg, ≈4,500 dalton and His, ≈ 4,500 dalton) could not be separated. One fragment (Lys, 1,500 dalton) could not be purified, but was analyzed in mixture with the Pro-fragment of 2,000 dalton. The tenth fragment is indicated by an N-terminal threonine together with the fragment having N-terminal isoleucine. The two smallest CNBr-fragments from barley have been sequenced and compared to the two smallest CNBr-fragments obtained from the large subunit of the spinach enzyme. One of the spinach fragments was identical to the Lys-fragment from barley whereas the other was homologous to the Ile-fragment from barley and revealed 3 amino acid differences between the two species. © 1979 Carlsberg Laboratory.