抄録
RuBisCO and phosphoribulokinase (PRK) are enzymes unique to Calvin cycle and we are interested in their evolution. In order to study the evolution of PRK, we have cloned three PRK homologues, glr2296, glr4426 and gll2122 (PRK-I, II and III, respectively) from the early diverging cyanobacterium, Gloeobacter violaceous. Analysis of PRK activities of purified proteins expressed in Escherichia coli reveals that PRK-I is the bona fide PRK possessing activity similar to other cyanobacterial PRKs, while PRKII does not possess any PRK activity. Interestingly, PRK-III possesses significant, albeit lower, PRK activity. In phylogenetic tree, PRK-III is placed in a clade with PRK homologues from methanogenic archaea. This protein could be an ancestral form of PRK which could have an archaeal origin. We discuss the properties of these two PRK homologues with respect to their amino acid sequences. The knowledge of true activity of PRK-III could suggest the probable course of PRK evolution.
