The activity utilizing the free SH-form of homocysteine with H2O2 has been found in rat blood plasma and erythrocyte lysates with the use of the glutathione peroxidase assay with hydrogen peroxide and 5,5'-dithiobis-(2-nitrobenzoic acid) and with the substitution of glutathione by homocysteine. The presence of rat plasma or erythrocyte lysate in a reaction mixture containing D,L-homocysteine, and H2O2 resulted in a marked acceleration of homocysteine concentration decrease (the decrease of homocysteine concentration was initiated by addition of hydrogen peroxide). The data obtained suggest the presence of homocysteine peroxidase activity in plasma and erythrocytes. The observed activity may be attributed to some known thiol-dependent enzymes. In the rat brain tissue, the level of the activity is extremely low (at the detection limit). The increase of the activity in blood components during post-embryonic ontogeny has also been shown. Probably, this activity contributes to low concentrations of free SH-form of homocysteine in the blood components.
Keywords: aminothiol, sulfhydryl groups, homocysteine peroxidase, activity, age