Purification and characterization of human platelet glutathione-S-
transferase
J Loscalzo and J Freedman
A glutathione-S-transferase was isolated and purified to homogeneity from
human platelets. With a combination of ammonium sulfate fractionation and
chromatographic methods, 0.2 mg of pure enzyme was obtained from 9 X 10(11)
platelets with a 12% recovery. The purified enzyme had a specific activity
of 7.5 U per milligram, representing an approximately 1,100-fold
purification. The enzyme was found to be anionic, with an isoelectric point
of 4.6. With reduced glutathione as a co-substrate, platelet
glutathione-S-transferase was most active with the synthetic substrate,
1-chloro-2,4-dinitrobenzene, less active with 1,2-dichloro-4-nitrobenzene,
and essentially inactive with nitroglycerin and
1,2-epoxy-3-(p-nitrophenoxy)-propane. The pH optimum for activity with
glutathione and 1-chloro-2,4-dinitrobenzene was 7.0. Indomethacin
(1-(p-chlorobenzoyl)-5-methoxy-2-methyindole-3-acetic acid), a
chlorobenzene derivative, noncompetitively inhibited human platelet
glutathione-S-transferase with an apparent KI of 0.23 mmol/L. This study
represents the first complete purification and characterization of a
glutathione-S-transferase from platelets. The presence of this enzyme in
the platelet, within which high concentrations of reduced glutathione
coexist, suggests the potential importance of the platelet in
detoxification reactions and in the synthesis of the glutathione adducts of
leukotriene metabolism.
Volume 67,
Issue 6,
pp. 1595-1599,
06/01/1986
Copyright © 1986 by The American Society of Hematology
