Immunologically and enzymatically distinct rat choline kinase isozymes.

The purification and characterization of choline kinase R1 expressed in Escherichia coli, using expression plasmid pKCK(H) constructed with rat liver choline kinase cDNA [Uchida, T. and Yamashita, S. (1992) J. Biol. Chem. 267, 10156-10162], were carried out. Choline kinase R1 was chromatographically, enzymatically, and immunologically distinct from rat brain choline kinase [Uchida, T. and Yamashita, S. (1990) Biochim. Biophys. Acta 1043, 281-288]. This report, for the first time, definitively demonstrates the presence of two types of choline kinase isozymes. Rat choline kinase was immunologically classified into choline kinases P and R. Choline kinase P was purified from rat brain as described previously. Choline kinase R was designated as the choline kinase generated from the choline kinase R gene for choline kinase R1. Choline kinases from cytosol were chromatographically separated into two fractions, that is, one passed through a Blue-Toyopearl column and the other was retained on it. The choline kinase retained on the Blue-Toyopearl column was highly purified from rat liver cytosol and characterized in this study, being found to comprise isoforms of choline kinase R, and a choline kinase which was immunologically similar to choline kinase P. Choline kinases P and R are co-distributed in rat tissues. The carcinogen, 3-methylcholanthrene, and hepatotoxic carbon tetrachloride increased the enzyme activity, and the transcript and protein levels of choline kinase R in rat liver. The relation of choline kinase isozymes to previously purified enzymes was discussed.