Rat heart pyrophosphate phosphohydrolase activities. Sub-cellular distribution, catalytic properties, and hormonal responses

James F. Soodsma, Robert C. Nordlie
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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).

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大鼠心脏焦磷酸盐磷酸水解酶活性。亚细胞分布、催化性质和激素反应
1.1. 研究了心脏组织匀浆中无机焦磷酸盐的代谢。亚细胞分布研究表明,主要的ppi代谢活性是Mg2+刺激的可溶性部分磷酸水解酶,在pH 7 ~ 7.5.3.3范围内活性最高。在Mg2+存在的情况下,在pH为7.3的颗粒组分中也检测到相对少量的活性。在没有添加Mg2+.4.4的情况下,所有馏分在pH 5.6时基本没有活性。ppi -葡萄糖磷酸转移酶活性1在任何亚细胞部分或匀浆中均未检测到。在催化方面,可溶性部分的活性与许多其他PPi磷酸水解酶相似(a)对Mg2+的绝对需求,(b)碱性pH最佳(心脏酶pH为7.3),以及(c)对Ca2+抑制的显著敏感性。四氧嘧啶糖尿病产生了大约。PPi磷酸水解酶活性下降33%。胰岛素治疗、肾上腺切除术或可的松治疗对酶活性水平没有统计学意义的改变。EDTA或额外的Mg2+可以逆转Ca2+的抑制作用,但补充PPi不能逆转。在Ca2+存在和不存在的情况下,柠檬酸盐对该系统均有抑制作用。根据观察(A)心脏PPi磷酸水解酶对Ca2+抑制极其敏感,(b)主动脉的钙化被PPi抑制(参考文献2),提出了一种延迟心脏血管系统和心脏附近钙化的反馈机制。
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