ACTIVITY AND CARBOXYLATION SPECIFICITY FACTOR OF MUTANT RIBULOSE 1,5-BISPHOSPHATE CARBOXYLASE OXYGENASE FROM ANACYSTIS-NIDULANS/

The values of molecular carboxylase activity k(cat) and carboxylation specificity factor tau for mutant ribulose 1,5-bisphosphate carboxylas e (rubisco) from Anacystis nidulans decreased as compared to those of the wild type recombinant rubisco. The substitution of five amino acid residues in rubisco large subunit Lys,Ala,Ser,Thr,Leu(339-343)Phe,Leu ,Met,Ile,Lys had k(cat) decreased by 90% and tau by 36.3%. The same pa rameters for mutants with the single replacements decreased: for Thr34 2Ile k(cat) by 40.5% and tau by 16.7%, and for mutant Leu343Lys k(cat) by 48.1% and tau by 18.5%. Mutant rubisco with three amino acid resud ues changed Val,Asp,Leu(346-348)Tyr,His,Thr was inactive. The substitu tion Leu326Ile decreased k(cat) by 54.4% and tau by 34.2%; and change Ser328Ala decreased k(cat) only by 5.6% but tau by 41.5%. Replacement Asn123His decreased k(cat) by 16.5%. Significance of the non conservat ive amino acid residues for carboxylase activity and ribulose-1,5-bisp hosphate partition is discussed.