Molecular cloning and expression analysis of PDK family genes in Xenopus laevis reveal oocyte-specific PDK isoform

Pyruvate dehydrogenase kinase (PDK) inactivates the multienzyme mitochondrial pyruvate dehydrogenase complex by the phosphorylation of three seryl residues in the pyruvate dehydrogenase moiety, and thus plays an important role in the control of glucose homeostasis. Genetically and biochemically distinct PDK family isozymes have been identified in mammalian species. In the present study, we demonstrate that the complete family of expressed PDK family genes in the tissues of the African clawed frog, Xenopus laevis, consists of four members, which are divided into two evolutionary groups. Xenopus PDKs (xPDKs) share an overall homology of about 70% to the human isoforms of PDK. The abundance of mRNAs for the four xPDK isoforms was analyzed by the real-time reverse transcriptase PCR technique in the various tissues of Xenopus laevis, including heart, lung, spleen, liver, kidney, skin, testis, oocytes, and eggs. Our data suggest that one of the xPDK isozymes can be referred to as an oocyte-specific xPDK. Functional differences between the xPDK isoforms are discussed, based on their different tissue-specific distributions and phylogenetic similarities to human PDKs.