{"database":"biostudies-other","file_versions":[],"scores":null,"additional":{"omics_type":["Unknown"],"volume":["258(3)"],"submitter":["Davidson AM"],"journal":["The Biochemical journal"],"pagination":["817-21"],"full_dataset_link":["https://www.ebi.ac.uk/biostudies/studies/S-EPMC1138437"],"abstract":["1. The pyrophosphatase activity in cytosolic and mitochondrial fractions of rat liver was 1.7 and 0.26 units/mg of protein respectively when assayed at 37 degrees C in the presence of physiological [Mg2+] (0.3 mM). 2. Approx. 80% of the mitochondrial pyrophosphatase was inaccessible to extramitochondrial PPi, of which 40% represented soluble matrix enzyme (0.38 unit/mg of matrix protein). 3. Ca2+ inhibited the soluble matrix enzyme; the effective K0.5 for inhibition increased as [Mg2+], an essential cofactor of the enzyme, increased. Measured values were 0.39, 1.15, 3.7, 8.3 and 12.5 microM at 0.04 mM-, 0.1 mM-, 0.3 mM-, 0.6 mM- and 1 mM-Mg2+ respectively. 4. The data were analysed by a kinetic model similar to that for yeast pyrophosphatase, which assumes the substrate to be MgPPi (Km 5 microM) with Mg2+ also activating at an additional site (K0.5 23 microM). Ca2+ inhibits through the formation of CaPPi, a strong competitive inhibitor (Ki 0.067 microM). 5. Heart mitochondria also contain a soluble matrix pyrophosphatase of similar activity to that of liver mitochondria and with the same sensitivity to [Ca2+]. 6. The data provide an explanation for the increase in mitochondrial PPi, mediated by Ca2+, which is responsible for the increase in matrix volume induced by gluconeogenic hormones [Davidson & Halestrap (1988) Biochem. J. 254, 379-384]."],"repository":["biostudies-other"],"data_source":["Europe PMC"],"pubmed_authors":["Halestrap AP","Davidson AM"],"additional_accession":[]},"is_claimable":false,"name":"Inhibition of mitochondrial-matrix inorganic pyrophosphatase by physiological [Ca2+], and its role in the hormonal regulation of mitochondrial matrix volume.","description":"1. The pyrophosphatase activity in cytosolic and mitochondrial fractions of rat liver was 1.7 and 0.26 units/mg of protein respectively when assayed at 37 degrees C in the presence of physiological [Mg2+] (0.3 mM). 2. Approx. 80% of the mitochondrial pyrophosphatase was inaccessible to extramitochondrial PPi, of which 40% represented soluble matrix enzyme (0.38 unit/mg of matrix protein). 3. Ca2+ inhibited the soluble matrix enzyme; the effective K0.5 for inhibition increased as [Mg2+], an essential cofactor of the enzyme, increased. Measured values were 0.39, 1.15, 3.7, 8.3 and 12.5 microM at 0.04 mM-, 0.1 mM-, 0.3 mM-, 0.6 mM- and 1 mM-Mg2+ respectively. 4. The data were analysed by a kinetic model similar to that for yeast pyrophosphatase, which assumes the substrate to be MgPPi (Km 5 microM) with Mg2+ also activating at an additional site (K0.5 23 microM). Ca2+ inhibits through the formation of CaPPi, a strong competitive inhibitor (Ki 0.067 microM). 5. Heart mitochondria also contain a soluble matrix pyrophosphatase of similar activity to that of liver mitochondria and with the same sensitivity to [Ca2+]. 6. The data provide an explanation for the increase in mitochondrial PPi, mediated by Ca2+, which is responsible for the increase in matrix volume induced by gluconeogenic hormones [Davidson & Halestrap (1988) Biochem. J. 254, 379-384].","dates":{"release":"1989-01-01T00:00:00Z","publication":"1989 Mar","modification":"2019-08-04T08:36:12Z","creation":"2019-08-04T08:36:12Z"},"accession":"S-EPMC1138437","cross_references":{"DOI":["10.1042/bj2580817 "]}}