Abstract
We determined the cDNA-derived amino acid sequences of two arginine kinases (AK1, AK2) from the annelid Sabellastarte indica, cloned the cDNAs into pMAL plasmid and expressed them in E. coli. The phylogenetic analyses suggested that Sabellastarte AKs have evolved from a CK-related gene, not from the usual AK gene. The recombinant Sabellastarte AK1 showed a broad specificity towards various guanidine compounds, while the Sabellastarte AK2 mainly showed stronger activity for both D- and L-arginine, a very unique substrate specificity not seen before in usual AKs. We isolated guanidino compounds from the body wall musculature of Sabellastarte, and found that the major compound is D-arginine with a concentration of 4.85 +/- 0.51 mmol/kg. From these results, we suggest strongly that in Sabellastarte, D-arginine is the major phosphagen substrate and that the AK2 with substrate specificity towards D-arginine, catalyzes the phosphorylation of D-arginine.
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