title: Isolation and characterization of glutathione S-transferase isozymes from sorghum.
abstract: Two glutathione S-transferase (GST) isozymes, A1/A1 and B1/B2, were purified from etiolated, O-1,3-dioxolan-2-yl-methyl-2,2,2, -trifluoro-4'-chloroacetophenone-oxime-treated sorghum (Sorghum bicolor L. Moench) shoots. GST A1/A1, a constitutively expressed homodimer, had a subunit molecular mass of 26 kD and an isoelectric point of 4.9. GST A1/A1 exhibited high activity with 1-chloro-2, 4, dinitrobenzene (CDNB) but low activity with the chloroacetanilide herbicide metolachlor. For GST A1/A1, the random, rapid-equilibrium bireactant kinetic model provided a good description of the kinetic data for the substrates CDNB and glutathione (GSH). GST B1/B2 was a heterodimer with subunit molecular masses of 26 kD (designated the B1 subunit) and 28 kD (designated the B2 subunit) and a native isoelectric point of 4.8. GST B1/B2 exhibited low activity with CDNB and high activity with metolachlor as the substrate. The kinetics of GST B1/B2 activity with GSH and metolachlor fit a model describing a multisite enzyme having two binding sites with different affinities for these substrates. Both GST A1/A1 and GST B1/B2 exhibited GSH-conjugating activity with ethacrynic acid and GSH peroxidase activity with cumene hydroperoxide, 9-hydroperoxy-trans-10, cis-12-octadecadienoic acid and 13-hydroperoxy-cis-9, trans-11-octadecadienoic acid. Both GST A1/A1 and GST B1/B2 are glycoproteins, as indicated by their binding of concanavalin A. Polyclonal antibodies raised against GST A1/A1 exhibited cross-reactivity with the B1 subunit of GST B1/B2. Comparisons of the N-terminal amino acid sequences of the GST A1, B1, and B2 subunits with other type I theta-GSTs indicated a high degree of homology with the maize GST I subunit and a sugarcane GST.
authors.affiliation: Plant Science Unit, University of Minnesota, St. Paul, Minnesota 55108, USA. gronw001@maroon.tc.umn.edu
authors.forename: J W
authors.initials: JW
authors.lastname: Gronwald
authors.forename: K L
authors.initials: KL
authors.lastname: Plaisance
mesh_terms: D000595:Amino Acid Sequence; D000937:Antigen-Antibody Reactions; D003429:Cross Reactions / Q000276:immunology; D002523:Edible Grain / Q000201:enzymology* / Q000276:immunology; D005982:Glutathione Transferase / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D006031:Glycosylation; D007527:Isoenzymes / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017421:Sequence Analysis; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: D007527:Isoenzymes; D005982:Glutathione Transferase