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Title: The glutathione S-transferases in human liver cytosol
Author: Stockman, Paul Kennedy
ISNI:       0000 0001 3486 3398
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1988
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A purification scheme is described for the basic and neutral glutathione S-transferases which occur in human liver. Three forms with basic isoelectric points, B-|Bi (pl'8.9), B-|B2 (pi 8.75) and B2B2 (pi 8.4) and two forms with neutral isoelectric points, N-j (pi 6.1) and N2 (pi 4.6), were obtained. Not every liver examined expressed transferase N-] or transferase N2^ An acidic enzyme from human lung, GST \ (pi 4.8), was included in the study for the purpose of comparison. Sodium dodecylsulphate/polyacrylamide-gel electro? phoresis demonstrated that each enzyme comprises two subunits of identical size. As a group the human glutathione S-transferases are composed of three distinct types of subunit with different molecular weights. The basic enzymes (B-]B-j, B1B2 and B2B2) were shown to have a subunit molecular weight of Mr 25 900, whereas, the neutral enzy? mes (N-] and N2) were found to comprise subunits of molecu? lar weight Mr 26 500 and the acidic transferase from lung ( X) was shown to be composed of subunits of molecular weight Mr 24 800. Antisera were raised against each of these enzymes and they were shown to cross-react only with enzymes from the same charge/molecular weight group. Contrary to previous work (Kamisaka e^t_ al_., ( 1975) Eur. J. Biochem. 60_: 153-161) data are presented to demonstrate that two distinct basic subunits are expressed in human liver (B^ and B2). Reversible dissociation and reassociation experiments demonstrated that transferases B-|Bi and B2B2 could be formed from trans? ferase B-1B2. Tryptic-di gest peptide 'maps' showed that the B-| and B2 subunits possess extensive sequence homo? logy, however, seven peptides were recovered from trans? ferase B-|Bi that were not recovered from transferase B2B2. Conversely, four peptides were recovered from transferase B2B2 that were not recovered from transferase B1B1. However, all these peptides were recovered from trans? ferase B*i B2; this is consistent with the hypothesis that B1B2 is a hybrid enzyme. A comparison of the substrate specificities of the enzymes demonstrated that transferases B -| B1, B-] B2 and B2B2 had a high peroxidase activity with cumene hydro? peroxide, transferases N-| and N2 had a high activity with trans-4 -phenyl-3 -but en-2- one and transferaseX had a high activity with ethacrynic acid. The IC50 values obtained for the basic enzymes demonstrated that the B1 subunit was much more potently inhibited by tributyltin acetate than the B2 subunit. The isoelectric point, molecular weight and high spe? cific activity with trans-4-phenyl-3-buten-2-one of trans? ferase N-| suggest that it is identical to transferase ]x, a form that has been previously characterised by Warholm et al., ( 1983) Biochemistry 22_: 361 0?3617- However, transferanse N2 is a novel enzyme that has not been described previously. The properties of this new enzyme indicate that it also belongs to the neutral group of enzymes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry