Back to Search
Start Over
Calcium and magnesium ions as effectors of adipose-tissue pyruvate dehydrogenase phosphate phosphatase.
- Source :
-
The Biochemical journal [Biochem J] 1974 May; Vol. 140 (2), pp. 225-37. - Publication Year :
- 1974
-
Abstract
- The metal-ion requirement of extracted and partially purified pyruvate dehydrogenase phosphate phosphatase from rat epididymal fat-pads was investigated with pig heart pyruvate dehydrogenase [(32)P]phosphate as substrate. The enzyme required Mg(2+) (K(m) 0.5mm) and was activated additionally by Ca(2+) (K(m) 1mum) or Sr(2+) and inhibited by Ni(2+). Isolated fat-cell mitochondria, like liver mitochondria, possess a respiration- or ATP-linked Ca(2+)-uptake system which is inhibited by Ruthenium Red, by uncouplers when linked to respiration, and by oligomycin when linked to ATP. Depletion of fat-cell mitochondria of 75% of their total magnesium content and of 94% of their total calcium content by incubation with the bivalent-metal ionophore A23187 leads to complete loss of pyruvate dehydrogenase phosphate phosphatase activity. Restoration of full activity required addition of both MgCl(2) and CaCl(2). SrCl(2) could replace CaCl(2) (but not MgCl(2)) and NiCl(2) was inhibitory. The metal-ion requirement of the phosphatase within mitochondria was thus equivalent to that of the extracted enzyme. Insulin activation of pyruvate dehydrogenase in rat epididymal fat-pads was not accompanied by any measurable increase in the activity of the phosphatase in extracts of the tissue when either endogenous substrate or (32)P-labelled pig heart substrate was used for assay. The activation of pyruvate dehydrogenase in fat-pads by insulin was inhibited by Ruthenium Red (which may inhibit cell and mitochondrial uptake of Ca(2+)) and by MnCl(2) and NiCl(2) (which may inhibit cell uptake of Ca(2+)). It is concluded that Mg(2+) and Ca(2+) are cofactors for pyruvate dehydrogenase phosphate phosphatase and that an increased mitochondrial uptake of Ca(2+) might contribute to the activation of pyruvate dehydrogenase by insulin.
- Subjects :
- Adenosine Triphosphate metabolism
Animals
Biological Transport
Calcium Radioisotopes
Enzyme Activation
Epididymis metabolism
Insulin metabolism
Ketone Oxidoreductases metabolism
Male
Mitochondria metabolism
Mitochondria, Liver metabolism
Myocardium enzymology
Nickel pharmacology
Phosphorus Radioisotopes
Pyruvates
Rats
Ruthenium
Strontium metabolism
Swine
Adipose Tissue enzymology
Calcium metabolism
Magnesium metabolism
Phosphoric Monoester Hydrolases metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 0264-6021
- Volume :
- 140
- Issue :
- 2
- Database :
- MEDLINE
- Journal :
- The Biochemical journal
- Publication Type :
- Academic Journal
- Accession number :
- 4375962
- Full Text :
- https://doi.org/10.1042/bj1400225