The Pivotal Glutathione Reductase

Glutathione is a tripeptide containing sulfhydryl groups combined with glutamic acid, cysteine and glycine. Glutathione has two forms, reduced (G-SH) and oxidized (G-S-S-G), and reduced glutathione accounts for the vast majority under physiological conditions. Glutathione reductase catalyzes the interconversion between the two types. The coenzyme of this enzyme is NADPH provided by the alternative metabolism of sugar phosphate.

Glutathione reductase is an enzyme EC.1.6.4.2 that catalyzes the reaction of oxidized glutathione (GS-S-G) to reduced form (GSH) using reduced NAD(P). The enzyme can be found in animal and plant tissues, microorganisms and yeast. The reaction is irreversible and will be inactivated upon dialysis, but activated by the addition of Mg2+ or Mn2+.

The enzymes in the mouse liver can almost only use NADP as a complementing enzyme, but the enzymes in the human erythrocytes also use NAD to function, and have no effect on cystine and homocysteine. It appears to act on the linkage of dehydrogenases and oxidases in plant tissues. When glutathione reductase GS-SG, NADP and chloroplast are mixed together and irradiated with light, oxygen will be released, which is the well-known Hill reaction.

The role of glutathione reductase:
GSH is an antioxidant that protects -SH in protein molecules from oxidation and protects sulfhydryl proteins and enzyme activity. Under the action of glutathione peroxidase, GSH can reduce H2O2 produced in cells to generate H2O. At the same time, GSH is oxidized to oxidized glutathione (GSSG), which in turn generates GSH under the catalysis of glutathione reductase.

Therefore, glutathione reductase can reduce oxidized glutathione (GSSG) to generate reduced glutathione (GSH), which is one of the key enzymes in the glutathione redox cycle. Glutathione reductase catalyzes the reduction of GSSG by NADPH to generate GSH, which helps to maintain the GSH/GSSG ratio in vivo. Glutathione reductase plays a key role in scavenging reactive oxygen species in response to oxidative stress, and GR is also involved in the ascorbic acid-glutathione cycle pathway. Glutathione reductase is distributed in many tissues and maintains sufficient intracellular levels of reduced glutathione (GSH). Loss of glutathione reductase makes cells more sensitive to oxidants and antibiotics.

For patients with liver damage, the detection of glutathione reductase can enable us to understand whether the function of the body's glutathione antioxidant system is sound. The reduction of glutathione reductase indicates that the detoxification function and antioxidant capacity of liver cells are decreased, and appropriate supplementation of exogenous GSH will help to recover. Normal or elevated glutathione reductase indicates normal liver detoxification and no need for exogenous GSH supplementation.

In addition, GSH can protect the sulfhydryl groups in certain proteins, such as protecting the sulfhydryl groups on the erythrocyte membrane from being damaged by oxides, and protecting the integrity of the erythrocyte membrane, thereby maintaining the normal structure and function of erythrocytes. Therefore, red blood cells are very sensitive to the loss of GSH, and in liver function tests, an increase in indirect bilirubin correlates with a decrease or depletion of GSH.