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KMID : 0376219750120020389
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Chonnam Medical Journal
1975 Volume.12 No. 2 p.389 ~ p.396
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Ecto-Enzymes of the Rabbit Erythrocytes
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Abstract
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A suspension of intact rabbit erythrocytes hydrolyzed added 5´-ribomononu-cleotides, ATP, NAD, and p-nitrophenyl phosphate under appropriate conditions. Evidence is presented that the hydrolyses are not due to artifacts such as breakage of the cells during the incubation period, indicating that the hydrolyses are being catalyzed by ecto-enzymes, i. e. enzymes on the plasma membrane with their active sites facing the external medium.
The ecto-5´-nucleotidase showed a single, sharp optimum pH at 7.0 in the absence and presence of Mg2+. The enzyme was inhibited by Mg2+ and fluoride, and acted more rapidly upon GMP than AMP, suggesting that ecto-5´-nucleotidase of the rabbit erythrocytes differs from the other 5´-nucleotidases from various tissues. Studies with various enzyme effectors also demonstrated that the ecto5´-nucleotidase, while possessing the capacity to hydrolyze p-nitrophenyl phosphate, is different from the ecto-ATPase.
Since NAD nucleotidase was found to be located only in the plasma membrane, the ecto-NAD-nucleotidase was considered to be more suitable as a marker enzyme for the plasma membrane of the rabbit erythrocytes, as compared with 5´-nucleotidase which is present both in the plasma membrane and in the cytoplasm of the erythrocytes.
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