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KMID : 0311119800210020129
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Yonsei Medical Journal
1980 Volume.21 No. 2 p.129 ~ p.136
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Biochemical and Physiological Characteristics of Ca-ATPase System of Rat Liver Mitochondria with Special Attention to the Effects of pH and Temperature
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Lee, Seung Mook
Hwang, Ae Ran/Kim, Hee Joong/Park, Yang Saeng
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Abstract
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The activity of Mg^(++) -dependent, Ca^(++) -activated adenosine triphosphatase (Ca-ATPase) of rat liver mitochondria was studied at varying medium compositions, pH and temperatures.
The enzyme system was characteristically sensitive to Ca^(++) concentration with a Km Ca of approximately 0.06 mM. The optimal concentration of Mg was about 1 mM, above which the enzyme activity was progressively inhibited. The inhibitory effect of high Mg^(++) concentrations appered to be due to the alteration of the Mg^(++)/ATP ratio. Variations in the Mg^(++)/ATP ratio affected Vmax but not the Km_(ATP). The pH optimum for enzyme activity increased as the incubation temperature decreased, but the optimal OH7H^(+) ratio of the medium was constant at around 0.1, regardless of temperature. The activity of the enzyme was not affected by La^(++) (0.01 - 1 mM) and Ruthenium red (2.5 - 10.0 ㎛).
These results indicate that 1) the enzymatic characteristics of the Ca-ATPase system in the rat liver mitochondria is typical of those from other tissue preparations, 2) the enzyme system maintains the most effective catalytic conformation at a fixed level of OH7H^(+) ratio of 0.1 when the temperature changes, and 3) the enzyme system may not play a role in the physiological transport of Ca^(++) in mitochondria.
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