Disorders of the Gamma Glutamyl Cycle

The gamma glutamyl cycle involves six and zymes. The biosynthesis of glutathione is catalyzed by gamma glutamyl cysteine synthetase and glutathione synthetase. The break down of the tripeptide is mediated by four enzymes. The initial step is catalyzed by gamma glutamyl transpeptidase. The gamma glutamyl residue is then released as 5-oxoproline, which is converted to glutamic by 5-oxoprolinase. The biosythesis of glutathione is feedback regulated, i.e., glutathione acts as an inhibitor to gamma glutamyl cysteine synthetase.

Glutathione has been postulated to participate in several fundamental functions, such as free radical scavenging, redox reactions, formation of deoxyribonucleotides, xenobiotic metabolism, and amino acid transport. Patients with genetic defects in the metabolism of glutathione are therefore likely to exhibit a variety of symptoms.

In diagnostic work it is essential to remember that erythrocytes contain an incomplete gamma glutamyl cycle gamma glutamyl transpeptidase, they lack both and 5-oxoprolinase.

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