Abstract
A cDNA clone coding for adenylate kinase 2B was isolated from fetal liver, and the expression of AK 2 was investigated in human tissues. The ORF in the cDNA clone for human AK2B predicted a protein comprising 232 amino acids (25.6 kDa). The features of AK2A and AK2B sequences in human were the same as those in the bovine system. Each of the recombinant proteins, AK2A and AK2B, was expressed in Escherichia coli cells, and the purified recombinant proteins were enzymatically active. The distribution of AK 2 transcripts in various human tissues was examined by Northern analysis. Unlike in the bovine system, it was found that the AK2A transcript was the major form of AK 2 mRNA species in all human tissues. The transcripts of AK 2 isozymes were relatively abundant in heart, liver, and also in skeletal muscle, where the expression level of AK 2 was known to be low. Western blot analysis of AK isozymes in human heart and skeletal muscle revealed that AK 2 protein was found only in heart, whereas AK 1 was detected in both tissues. These tissue-specific expressions of the AK isozymes in human might suggest the presence of organ-specific regulation of the AK 2 gene including a post-transcriptional control in skeletal muscle.
