Ascorbate‐Induced Oxidative Inactivation of Zn²⁺‐Glycerophosphocholine Cholinephosphodiesterase

Abstract

Zn2-glycerophosphocholine cholinephosphodiesterase, responsible for the conversion of glycerophosphocholine into glycerol and phosphocholine, was inactivated during incubation with ascorbic acid at 38°C. The inclusion of copper ions or Fe2~accelerated the ascorbateinduced inactivation, with Cu2~or Cubeing much more effective than Fe2~, suggestive of ascorbate-mediated oxidation. Dehydroascorbic acid had no effect on the phosphodiesterase, but H 202 inactivated the enzyme in a concentration-dependent manner. Also, the enzyme was inactivated partially by a superoxide anion-generating system but not an HOCI generator. In support of involvement of H202 in the ascorbate action, catalase and superoxide dismutase expressed a complete and a partial protection, respectively. However, hydroxy radical scavengers such as mannitol, benzoate, or dimethyl sulfoxide were incapable of preventing the ascorbate action, excluding the participation of extraneous 0H. Although p-nitrophenylphosphocholine exhibited a modest protection against the ascorbate action, a remarkable protection was expressed by amino acids, especially by histidine. In addition, imidazole, an electron donor, showed a partial protection. Separately, when~-induced inactivation of the phosphodiesterase was compared with the ascorbate-mediated one, the protection and pH studies indicate that the mechanism for the ascorbate action is different from that for the Cu 2~action. Here, it is proposed that Zn2~-gIycerophosphocholinecholinephosphodiesterase is one of brain membrane proteins susceptible to oxidative inactivation.

Vitamin C Deficiency Activates the Purine Nucleotide Cycle in Zebrafish

“…Glycerophospholipid Metabolism-The inhibitory effect of AA on GlyPhCh choline phosphodiesterase, an enzyme that converts GlyPhCh into glycerol and phosphocholine, has been explored previously in vitro (40). A recent study of AA deficiency in the Gulo Ϫ/Ϫ mice revealed differentiating levels of the downstream products of GlyPhCh choline phosphodiesterase, glycerol, phosphocholine, and choline (41).…”

Beneficial effect of oleoylated lipids on paraoxonase 1: protection against oxidative inactivation and stabilization

“…The introduction of hypolipidaemic drugs or their metabolites significantly enhanced the ability of PON1 to reduce the level of cholesterylester hydroperoxides in oxidized LDL [28]. Another strategy to protect enzymes from the inactivation by ROS or lipid peroxidation products would be the employment of substrates, inhibitors or regulators [29,30]. However, an earlier study indicated that the inhibitors of PON1 might be inappropriate for this purpose as demonstrated from the negative role of PON1 inhibitors, such as PD65950, in preventing LDL oxidation [31].…”

Purification and Characterization of Lysophospholipase C from Pig Brain

“…Additionally, GPC phosphocholine phosphodiesterase is very susceptible to Cu 2? /ascorbate inactivation [28], but lysoPLC is not. Besides, GPC phosphocholine phosphodiesterase possesses a molecular weight of 74 kDa [12], whereas that of lysoPLC is 65 kDa.…”

“…Actually, the procedures for the isolation and purification of brain lysoPLC are similar to those which had been used for the preparation for the purified alkaline phosphatase [4,27]. Therefore, it is supposed that brain lysoPLC may be one of enzymes, located on the external site of cell membrane, such as alkaline phosphatase [4,5], 5 0 -nucleotidase, phosphodiesterase and lysophospholipases [28]. Actually, lysoPLC activity comigrated with alkaline phosphatase activity in Concanavalin A sepharose 4B chromatography, indicating that lysoPLC corresponds to a glycoprotein.…”