{"title":"Rat heart pyrophosphate phosphohydrolase activities. Sub-cellular distribution, catalytic properties, and hormonal responses","authors":"James F. Soodsma, Robert C. Nordlie","doi":"10.1016/0926-6593(66)90042-7","DOIUrl":null,"url":null,"abstract":"<div><p></p><ul><li><span>1.</span><span><p>1. Inorganic pyrophosphate metabolism in cardiac tissue homogenates has been investigated.</p></span></li><li><span>2.</span><span><p>2. A sub-cellular distribution study indicated that the predominant PP<sub>i</sub>-metabolizing activity is Mg<sup>2+</sup>-stimulated soluble-fraction phosphohydrolase which is maximally active in the range pH 7–7.5.</p></span></li><li><span>3.</span><span><p>3. Relatively small amounts of activity also were detected in particulate fractions at pH 7.3 in the presence of Mg<sup>2+</sup>. Activity was essentially absent from all fractions at pH 5.6 without added Mg<sup>2+</sup>.</p></span></li><li><span>4.</span><span><p>4. PP<sub>i</sub>-glucose phosphotransferase activity<sup>1</sup> could not be detected in any sub-cellular fraction or in homogenates.</p></span></li><li><span>5.</span><span><p>5. Catalytically, the soluble fraction activity resembles a number of other PP<sub>i</sub> phosphohydrolases with respect to (a) absolute requirement for Mg<sup>2+</sup>, (b) alkaline pH optimum (pH 7.3 for the heart enzyme), and (c) marked sensitivity to Ca<sup>2+</sup> inhibition.</p></span></li><li><span>6.</span><span><p>6. Alloxan diabetes produced an approx. 33% drop in PP<sub>i</sub> phosphohydrolase activity. Insulin administration, adrenalectomy, or cortisone treatment did not produce statistically significant changes in levels of enzymic activity.</p></span></li><li><span>7.</span><span><p>7. Inhibition due to Ca<sup>2+</sup> was reversed by EDTA or additional Mg<sup>2+</sup>, but not by supplemental PP<sub>i</sub>. Citrate inhibited the system both in the presence and absence of Ca<sup>2+</sup>.</p></span></li><li><span>8.</span><span><p>8. A feedback mechanism for retardation of calcification in the vascular system of and near the heart is suggested based on the observations that (a) heart PP<sub>i</sub> phosphohydrolase is extremely sensitive to Ca<sup>2+</sup> inhibition, and (b) calcification of the aorta is inhibited by PP<sub>i</sub> (ref. 2).</p></span></li></ul></div>","PeriodicalId":100160,"journal":{"name":"Biochimica et Biophysica Acta (BBA) - Enzymology and Biological Oxidation","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"1966-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/0926-6593(66)90042-7","citationCount":"10","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Biochimica et Biophysica Acta (BBA) - Enzymology and Biological Oxidation","FirstCategoryId":"1085","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/0926659366900427","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 10
Abstract
1.
1. Inorganic pyrophosphate metabolism in cardiac tissue homogenates has been investigated.
2.
2. A sub-cellular distribution study indicated that the predominant PPi-metabolizing activity is Mg2+-stimulated soluble-fraction phosphohydrolase which is maximally active in the range pH 7–7.5.
3.
3. Relatively small amounts of activity also were detected in particulate fractions at pH 7.3 in the presence of Mg2+. Activity was essentially absent from all fractions at pH 5.6 without added Mg2+.
4.
4. PPi-glucose phosphotransferase activity1 could not be detected in any sub-cellular fraction or in homogenates.
5.
5. Catalytically, the soluble fraction activity resembles a number of other PPi phosphohydrolases with respect to (a) absolute requirement for Mg2+, (b) alkaline pH optimum (pH 7.3 for the heart enzyme), and (c) marked sensitivity to Ca2+ inhibition.
6.
6. Alloxan diabetes produced an approx. 33% drop in PPi phosphohydrolase activity. Insulin administration, adrenalectomy, or cortisone treatment did not produce statistically significant changes in levels of enzymic activity.
7.
7. Inhibition due to Ca2+ was reversed by EDTA or additional Mg2+, but not by supplemental PPi. Citrate inhibited the system both in the presence and absence of Ca2+.
8.
8. A feedback mechanism for retardation of calcification in the vascular system of and near the heart is suggested based on the observations that (a) heart PPi phosphohydrolase is extremely sensitive to Ca2+ inhibition, and (b) calcification of the aorta is inhibited by PPi (ref. 2).