Oxoprolinase

NUCLEOSIDE DIPHOSPHATE KINASE 5-OXOPROLINASE PHENYLALANINE RACEMASE 1-PHOSPHATIDYLINOSITOL 4-KINASE PHOSPHATIDYLINOSITOL-4-PHOSPHATE 5-KINASE... 

KINETIC ISOTOPE EEEECTS 5-OXOPROLINASE Oxyanion intermediate,... 

PYRIDOXAL 4-DEHYDROGENASE PYRIMIDINE DIMER DNA GLYCOSYLASE Pyroglutamase (ATP-hydrolyzing), 5-OXOPROLINASE... 

The significance of the y-glutamyl cycle is not fully understood. However, the finding of a mentally retarded individual who excretes 25-50 g / day of 5-oxoproline in the urine (possibly because of a defective 5-oxoprolinase) suggests that the pathway is a very active one.111 A few persons deficient in y-glutamyl transpeptidase have been found. They excrete glutathione and have a variety of medical problems.109... 

What are the functions of the two water molecules that are utilized by the enzyme 5-oxoprolinase (fig. 22.15) ... 

OTZ is a pro-drug of cysteine and is rapidly converted by 5-oxoprolinase to cysteine in vivo... 

GSH-peroxidase because of detoxification of putatively increased amounts of hydroperoxides. Therefore, it seems crucial to protect cells from loss of antioxidants and potent reducing substances, such as NADPH or NADH. In turn, depletion of cells from ATP by inhibition of oxidative phosphorylation could result in decreased activity of 5-oxoprolinase, glutamyl-cysteine-synthetase and GSH synthetase, all known to be dependent on ATP (Meister, 1991), resulting in impaired detoxification mechanisms and subsequent cell damage because of oxidative stress. 

Oxoprolinase has been identified in several higher plants (compare Section VII. 1.2.) 400). 

Mazelis, M., and R. K. Creveling 5-Oxoprolinase (L-pyroglutamate hydrolase) in higher plants. Plant Physiol. 62, 798 (1978). 

Oxoprolinase deficiency has been identified in eight patients, who lack a consistent clinical syndrome. Urinary excretion of 5-oxoproline is elevated but less than in glutathione synthetase deficiency. Erythrocytes contain an incomplete y-glutamyl cycle they lack both y-glutamyl transpeptidase and 5-oxoprolinase. 

Fig. 9. Proposed pathways for the synthesis and catabolism of glutathione (y-glutamylcysteinyl-glycine) i n plants. The enzymes involved in glutathione synthesis are (1) >.glutamylcysteine synthetase and (2) glutathione synthetase. The enzymes involved in glutathione catabolism are (3) glutathione carboxypeptidase, (4) yglutamylcyclotransferase, and (5) 5-oxoprolinase. (After Rennen-beig, 1987.)...

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