Effect of 60Co gamma-irradiation on the reaction of mixed disulphides of mercaptoethylguanidine with enzymes of rat-liver cytoplasm.

A theoretical assumption of Eldjarn and Pihl suggests that mixed disulphides formed by radioprotective aminothiols and protein SH-groups can be broken down by enzymes in the organism, and the native structure of the macromolecules restored. Irradiation should enhance this effect. In our experiments, mixed disulphides of mercaptoethylguanidine (MEG) and albumin/haemoglobin were split by the soluble enzyme fraction of rat-liver homogenate (cytosol). The liberation of the radioprotector MEG is brought about by small molecules; dialysed cytosol has no effect, nor has the suspension of particles of mitochondria. On irradiation with doses in the 0-1--5-0 Mrad range, the mixed disulphide bridge is stabilized and made more resistant to splitting. Increased resistance up to 700 per cent with albumin-MEG and 160 per cent with haemoglobin (Hb)-MEG mixed disulphide was observed compared with the unirradiated control.