Diagnostic and Toxicological Aspects of Glutathione S-Transferases

Abstract

Three aspects of the physiological function of the enzymes, the GSH S-transferases, have been examined. These were...... 1) The Inhibition of the Enzymes by Reaction Products and Their Derivatives GSH S-transferase activities with 1-chloro-2,4-dinitrobenzene, 1,2-dichloro-4-nitrobenzene, p-nitrobenzyl chloride and 1,2-epoxy-3-(p-nitrophenoxy)propane, in decreasing order, were inhibited by their reaction products - GSH conjugates. S-(hexyl)-L-glutathione was the most potent inhibitor compared to benzyl- and DNP- derivatives. Inhibition studies on purified ligandin showed that S-(hexyl)-L-glutathione had a Ki of (3.5 ± 0.5) x 10-5M with respect to GSH and (4.7 ± 0.7) x 10-5M with respect to CDNB. The Ki of S-(benzyl)-L-glutathione was (20.5 ± 2.4) x 10-5M and (10.1 ± 0.7) x 10-5M with respect to GSH and CDNB respectively. 2) The Effects of GSH on the Bindinq of Liqands to Serum Albumin and GSH S-Transferase (Ligandin) The binding affinity of ligandin was lowered in the presence of GSH (2 mM) at pH 7.4. The binding of ligands such as BSP, BSP-GSH, DBSP, amaranth and bromophenol blue to a mixture of rat plasma/liver cytosol by gel filtration (Sephadex G-100) showed the reduced binding of the ligands to both albumin and ligandin in the presence of GSH. The binding constant for the binding of amaranth to purified ligandin was reduced by 90% in the presence of GSH (2 mM). 3) The Utility of Serum GSH S-Transferase measurements in the Diagnosis of Liver Disease Experiments with an animal (Wistar albino rat) model using CCl4, to induce liver damage produced a rise in serum ligandin. The serum level reached a peak at 40 hours with 32 x control level. The serum level returned to normal level by 64 hours. Parallel estimations of serum LDH, AP and GGTP showed no correlation between serum GST and AP, nor between serum GST and GGTP. There was significant correlation between serum GST and LDH (r = 0.88, p<0.001). There was no correlation between any of the hepatic enzyme activities. There was a good correlation between serum GST and GPT,r = 0.41836 (p< 0.0001) and a small correlation between serum GST and GGTP,r was 0.11784 (p< 0.04) in random sampling of pathological human sera. No correlation was found between serum GST and other liver function tests. However, when the samples were separated into homogeneous groups, good correlation was found between serum GST and other parameters such as GOT. There was inverse correlation between serum GST and TB. The measurement of serum GST has limited use for routine screening of liver dysfunction.