An enzyme from rat liver catalysing conjugations with glutathione. 2. Replacement of nitro groups

Abstract

2-methylpropan-2-ol-4 25N-ammonia (4:1, v/v). Many solvent systems for these compounds have been proposed (see, for example, Kubota, 1961); the information is given because the system seems to be a very versatile one. It was used (Vining & Taber, 1957) for oc-amino acids and c-hydroxy acids, and later (Russell, 1960) for N-methyl-amino acids. It is a stable one-phase system, and gives compact spots with DNP-derivatives, the R. values lying between 0.1 and 0-8 approximately. The DNP-derivatives of leucine and isoleucine are particularly well separated. SUMMARY 1. Solutions of DNP-amino acids and-peptides in dilute aqueous sodium hydrogen carbonate were examined photochemically. 2. The a-DNP-amino acids were all rapidly decomposed by light with the exception of DNPtryptophan; $., 8-and c-DNP-amino acids were stable, and DNP-peptides were either stable or decomposed much more slowly than a-DNP-amino acids. 3. Formation of 4-nitro-2-nitrosoaniline on photolysis appeared to be a property exclusively of (lerivatives possessing the structure DNP *NH* CRR' CO2H, but not all compounds possessing this structure yield 4-nitro-2-nitrosoaniline. 4. The solvent system 2-methylpropan-2-ol-4 25N-ammonia (4:1, v/v) was useful for the paper chromatography of DNP-amino acids.

The Role of Glutathione and Glutathione S‐Transferases in Mercapturic Acid Biosynthesis

“…In no case has a glutathione adduct or the mercapturic acid derivative been found to be more toxic than the precursor. Combes and Stakelum (1961); (3) Al-Kassab, Boyland and Williams (1963); (4) Boyland and Williams (1965); (5) Johnson (1966a); (6) Suga, Ohata, Kumaoka, and Akagi (1967); (7) Boyland and Chasseaud (1967) ; (8) Boyland and Chasseaud (1968) ; (9) Chasseaud (1967); (10) Fukami and Shishido (1966); (11) Hutson, Pickering, and Donninger (1968); (12) Heppel and Hilmoe (1950); (13) Needleman and Hunter (1965); (14) Lipke and Kearns (1959); (15) Ganther (1966).…”

“…Measurement a t this new wavelength gives a direct reading of the enzymic reaction occurring. Other glutathione 8-transferases are generally estimated by measuring substrate loss (Boyland and Williams, 1965;Johnson, 1966a;Boyland and Chasseaud, 1967), release of labile groups (Al-Kassab et al, 1963;Boyland and Williams, 1965;Johnson, 1966a), or the reaction products are detected (Booth et al, 1961) or estimated (Suga, Ohata, Kumaoka, and Akagi, 1967) by chromatography.…”

“…Compounds of this type, which are metabolized to mercapturic acids in rabbits (Table V) include mono-, di-, and trihalogenonitrobenzenes Thorpe, 1955a,b, l956,1957a, 195th). This same enzyme probably conjugates glutathione with certain tetrahalogenonitrobenzenes that are metabolized to mercapturic acids (Bray, Hybs, James, and Thorpe, 1953;Betts, James, and Thorpe, 1955) by repIace- ment of nitro groups (Al-Kassab et al, 1963). The nitro group is also lost during mercapturic acid biosynthesis from certain trihalogenonitrobenzenes and from pentahalogenonitrobenzene (Betts, James, and Thorpe, 1955;Betts, Bray, James, and Thorpe, 1957), and it appears that the nitro group is lost where it is flanked by halogen atoms and there is another halogen atom in the ring, viz., k and 7.…”

“…The reactions of glutathione with 4-nitropyridine N-oxide (1 1) and the carcinogenic 4-nitroquinoline N-oxide (12) are probably catalyzed by glutathione 8-aryltransferase (Al-Kassab et al, 1963) : the latter reacts rapidly with thiols even in the absence of the enzyme (Nakahara and Fukuoka, 1959). NO* I NO2 I Conjugation of sulfobromophthalein ( 5 ) with glutathione (Combes and Stakelum, 1961) is possibly catalyzed by glutathione S-aryltransferase.…”

Glutathione S-aralkyltransferase

“…Reactions catalysed by known glutathione S-transferases are of two types: first, addition of GSH catalysed by glutathione S-alkenetransferases and S-epoxidetransferase; secondly, replacement by GSH catalysed by the remaining enzymes (Table 1). Apart from foreign compounds that are similar to substrates described in the present paper, glutathione Stransferases catalyse the reactions of GSH wvith fl-propiolactone (Johnson, 1966), some organophosphorus compounds (Fukami & Shishido, 1966;Hutson, Pickering & Donninger, 1968;Morello, Vardanis & Spencer, 1968), activated aryl nitro compounds (Al-Kassab et al 1963), some nitrofurans (Williams, 1968), sulphobromophthalein (Combes & Stakelum, 1961) and some alicyclic epoxides (Boyland & Williams 1965). The properties and identity of these glutathione Stransferases are largely unknown, but some may be identical with the enzymes described in Table 1.…”