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Purified γ-glutamyl transpeptidases from tomato exhibit high affinity for glutathione and glutathione S-conjugates
被引:66
作者:
Martin, MN
[1
]
Slovin, JP
[1
]
机构:
[1] USDA ARS, Beltsville Agr Res Ctr, Climate Stress Lab, Beltsville, MD 20705 USA
关键词:
D O I:
10.1104/pp.122.4.1417
中图分类号:
Q94 [植物学];
学科分类号:
071001 ;
摘要:
gamma-Glutamyl transpeptidases (gamma GTases) are the only enzymes known to hydrolyze the unique N-terminal amide bonds of reduced glutathione (gamma-L-glutamyl-cysteinyl-glycine), oxidized glutathione, and glutathione S-conjugates. Two gamma GTases (I and II) with K-m values for glutathione of 110 and 90 mu M were purified 2,977-fold and 2,152-fold, respectively, from ripe tomato (Lycopersicon esculentum) pericarp. Both enzymes also hydrolyze dipeptides and other tripeptides with N-terminal, gamma-linked Glu and the artificial substrates gamma-L-glutamyl-p-nitroanilide and gamma-L-glutamyl(7-amido-4-methylcoumarin). They transfer the glutamyl moiety to water or acceptor amino acids, including L-Met, L-Phe, L-Trp, L-Ala, or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid. gamma GTase I and II were released from a wall and membrane fraction of a tomato fruit extract with 1.0 M NaCl, suggesting that they are peripheral membrane proteins. They were further purified by acetone precipitation, Dye Matrex Green A affinity chromatography, and hydrophobic interaction chromatography. The two gamma GTases were resolved by concanavalin A (Con A) affinity chromatography, indicating that they are differentially glycosylated. The native and SDS-denatured forms of both enzymes showed molecular masses of 43 kD.
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页码:1417 / 1426
页数:10
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