A novel arginine kinase from the shrimp Neocaridina denticulata: the fourth arginine kinase gene lineage.

Arginine kinases (AK) evolved independently at least three times: first at an early stage of phosphagen kinase evolution (typical AK), second from the cytoplasmic creatine kinase (CK) gene later in metazoan evolution (Stichopus AK) and third from the mitochondrial CK gene in the course of annelid radiation (Sabellastarte AK). Here, we present a possible fourth AK lineage. We amplified cDNA encoding three AKs (AK1, AK2 and AK3) from the shrimp Neocaridina denticulata, and determined their amino acid sequences (355-356 residues).