Abstract
Creatine kinase (CK; EC 2.7.3.2) isoenzymes play prominent roles in energy metabolism. Nuclear genes encode three known CK subunits: cytoplasmic muscle (MCK), cytoplasmic brain (BCK), and mitochondrial (MtCK). We have isolated the gene and cDNA encoding human placental MtCK. By using a dog heart MCK cDNA-derived probe, the 7.0-kb EcoRI fragment from one cross-hybridizing genomic clone was isolated and its complete nucleotide sequence determined. A region of this clone encoded predicted amino acid sequence identical to residues 15-26 of the human heart MtCK NH2-terminal protein sequence. The human placental MtCK cDNA was isolated by hybridization to a genomic fragment encoding this region. The human placental MtCK gene contains 9 exons encoding 416 amino acids, including a 38-amino acid transit peptide, presumably essential for mitochondrial import. Residues 1-14 of human placental MtCK cDNA-derived NH2-terminal sequence differ from the human heart MtCK protein sequence, suggesting that tissue-specific MtCK mRNAs are derived from multiple MtCK genes. RNA blot analysis demonstrated abundant MtCK mRNA in adult human ventricle and skeletal muscle, low amounts in placenta and small intestine, and a dramatic increase during in vitro differentiation induced by serum-deprivation in the non-fusing mouse smooth muscle cell line, BC3H1. These findings demonstrate coordinate regulation of MtCK and cytosolic CK gene expression and support the phosphocreatine shuttle hypothesis.
Highlights
From the Departments of Biological Chemistry, Medicine,and Pediatrics, Washington University School of Medicine, St
Based upon the lack of encode three known Creatine kinases (CK) subunits: cytoplasmic muscle immunological cross-reactivity and differences in amino acid (MCK), cytoplasmic brain (BCK), and mitochondrial composition, electrophoretic mobility, and peptide maps of (MtCK).We have isolated the gene and cDNA encoding purified subunits, it has been proposed that three CK genes human placental MtCK
Resi- period [8].MtCK activity is detected in fetal lamb dues 1-14 of human placental MtCK cDNA-derived heart insmall amounts andundergoes further induction post
Summary
MtCK [10] in which myoblasts fuse into multinucleated myotubes. mRNA in adult human ventricle and skeletalmuscle, In addition, differentiating skeletal muscle tissueand mylow amounts in placenta and small intestine, and a ogenic cell cultures exhibit an overlapping isoenzyme transidramatic increase during in vitro differentiation in- tion from BCK in embryonic myoblasts to predominantly duced by serum-deprivation in the non-fusing mouse smooth muscle cell line, BCsH1. MRNA in adult human ventricle and skeletalmuscle, In addition, differentiating skeletal muscle tissueand mylow amounts in placenta and small intestine, and a ogenic cell cultures exhibit an overlapping isoenzyme transidramatic increase during in vitro differentiation in- tion from BCK in embryonic myoblasts to predominantly duced by serum-deprivation in the non-fusing mouse smooth muscle cell line, BCsH1. These findings demonstrate coordinate regulationof MtCK and cytosolic CK gene expression and support the phosphocreatine shuttle hypothesis. In detail previously [35]
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