Yonsei Med J.  1980 Dec;21(2):129-136. 10.3349/ymj.1980.21.2.129.

Biochemical and Physiological Characteristics of Ca-ATPase System of Rat Liver Mitochondria with Special Attention to the Effects of pH and Temperature

• Lee SM
• Hwang AR
• Kim HJ
• Park YS

• KMID: 692906
• DOI: http://doi.org/10.3349/ymj.1980.21.2.129

Abstract

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 KmCa of approximately 0.06 mM. The optimal concentration of Mg was about l mM, above which the enzyme activity was progressively inhibited. The inhibitory effect of high Mg++ concentrations appeared to be due to the alteration of the Mg++/ATP ratio. Variations in the Mg++/ATP ratio affected Vmax but not the KmATP. The pH optimum for enzyme activity increased as the incubation temperature decreased, but the optimal OH-/H+ 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 microM). 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 OH-/H+ 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.

MeSH Terms

Animal
Ca(2+)-Transporting ATPase/metabolism*
Calcium/pharmacology
Enzyme Activation/drug effects
Female
Hydrogen-Ion Concentration
Magnesium/pharmacology
Male
Mitochondria, Liver/enzymology*
Rats
Temperature