CLONING AND EXPRESSION OF HUMAN ADENYLATE KINASE-2 ISOZYMES - DIFFERENTIAL EXPRESSION OF ADENYLATE KINASE-1 AND KINASE-2 IN HUMAN MUSCLE TISSUES

A cDNA clone coding for adenylate kinase 2B was isolated from fetal li ver, and the expression of AK2 was investigated in human tissues. The ORF in the cDNA clone for human AK2B predicted a protein comprising 23 2 amino acids (25.6 kDa), The features of AK2A and AK2B sequences in h uman were the same as those in the bovine system, Each of the recombin ant proteins, AK2A and AK2B, was expressed in Escherichia coli cells, and the purified recombinant proteins were enzymatically active, The d istribution of AK2 transcripts in various human tissues was examined b y Northern analysis, Unlike in the bovine system, it was found that th e AK2A transcript was the major form of AK2 mRNA species in all human tissues, The transcripts of AK2 isozymes were relatively abundant in h eart, liver, and also in skeletal muscle, where the expression level o f AK2 was known to be low, Western blot analysis of AK isozymes in hum an heart and skeletal muscle revealed that AK2 protein was found only in heart, whereas AK1 was detected in both tissues, These tissue-speci fic expressions of the AK isozymes in human might suggest the presence of organ-specific regulation of the AK2 gene including a post-transcr iptional control in skeletal muscle.