Homoglutathione

Breaux. E.I.. Patanella. I.E.. and Sanders. E.F. Chloroacetanilide herbicide selectivity analysis of glntathione and homoglutathione in tolerant, snsceptible and safened seedlings. J. Agric. Food Chem., 35(4) 474-478.1987. 

Grill, E., Gekeler, W., Winnacker, E.-L. Zenk, M.H. (1986b). Homo-phytochelatins are heavy metal binding peptides of homoglutathione containing Fabales. FEBS Letters 205, 47-50. 

Klapheck, S. (1988). Homoglutathione isolation, quantification and occurrence in legumes. Physiologia Plantarum 74, 727-32. 

Frear, D.S., H.R. Swanson, and E.R. Mansager (1985). Alternate pathways of metribuzin metabolism in soybean Formation of V-glucoside and homoglutathione conjugates. Pestic. Biochem. Physiol., 23 56-65. 

D, which Is structurally similar to MCPA, appeared to be Inco-porated into lignin (255). This was in sharp contrast to MCPA metabolism in wheat. Carboxln (aniline-l4C) metabolism in peanut cell suspension culture and the fruit of whole peanut plants is an example of tissue variation. In peanut cell suspension culture, only 2.7% of the carboxln was incorporated Into bound residue, but In the fruit of whole plants, 21% Incorporation into bound residue was observed (121). The metabolism of metrlbuzln In tomato and soybean Is an excellent example of species variation. In tomato, metrlbuzln was rapidly metabolized to N-glucosldes and only 2% was Incorporated into bound residue, but In soybean, metrlbuzln was metabolized slowly by homoglutathione conjugation and 20-30% of the metrlbuzln was incorporated into bound residue (46.95). 

Fast atom bombardment has also been used successfully with metabolites related to or derived from glutathione conjugates, e.g. a homoglutathione soybean metabolite (40) and mammalian mercapturates and cysteinyl conjugates (24, 41-44). 

Figure 9.5 The metabohsm of glutathione and homoglutathione conjugates in higher plants. [Reproduced from G. L. Lamoreux, R. H. Shimabukuro, and D. S. Frear Glutathione and Glucoside Conjugation in Herbicide Selectivity , in J. C. Caseley, G. W. Cussans, and R. K. Atkin, Eds., Herbicide Resistance in Weeds and Crops, Butterworth-Heinemann Ltd., Oxford, pp. 227-262. Copyright 1991, with permission from Elsevier.]...

The metabolism of triazolopyrimidine sulfonanilides (1-4) in plants has been reviewed [23, 24]. It has been shown that diclosulam (3) and doransulam-methyl (4) are rapidly metabolized in soybeans by facile conjugation with homoglutathione which displaces the 7-fluoro substituent (Fig. 2.4.1) [25]. This mechanism was found to only occur in soybeans for 3 and 4. Oxidation at the 4-position of the aniline ring occurs rapidly in maize for 3 and 4. In wheat, 4 undergoes O-dealkylation of 5-ethoxy followed by glucose conjugation and oxidation at the 4-position of the aniline ring occurs for 3 [25]. 

One exception is known. Homoglutathione (y-glutamyIcysteinyl-/3-alanine) is present at a much higher concentration than glutathione in mung beans (Carnegie, 1963). 

Aryl hydroxylation (1) Deesterification (2) Homoglutathione 1 conjugation (3) S02NHCNH— (N) i y / Aliphatic T hydroxylation (4) / Sulfonamide Urea Cleavage (7) hydrolysis (6) 0-Demethylation (5) ... 

This enzyme is very active in plants, especially in leaf tissue. In some legumes the concentration of glutathione is extremely low and the closely related tripeptide y-L-glutamyl-L-cysteinyl-L-alanine (referred to as homoglutathione) is the major soluble thiol. 

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