Insight into naphthoquinone metabolism: beta-glucosidase-catalysed hydrolysis of hydrojuglone beta-D-glucopyranoside.
In plants, the naphthoquinone juglone is known to be involved in pathogenic defence mechanisms, but it may also take part in plant developmental processes. This naphthoquinone can accumulate in a glycosylated form, namely hydrojuglone beta-d-glucopyranoside. The structural configuration of this compound was shown to be 1, 5-dihydroxy-4-naphthalenyl-beta-d-glucopyranoside by means of MS, NMR and nuclear Overhauser effect spectroscopy analyses. A hydrojuglone beta-d-glucopyranoside beta-glucosidase (EC 3.2.1.21) was purified to homogeneity from Juglans regia L. The enzyme catalysed the release of juglone from hydrojuglone beta-d-glucopyranoside with high specificity and showed Michaelis-Menten kinetics with Km=0.62 mM and Vmax=14.5 microkat/mg of protein. This enzyme also showed a higher activity towards beta-d-fucosyl than beta-d-glucosyl bonds. The purified enzyme had an apparent Mr of 64000 by SDS/PAGE and a pI 8.9 by isoelectrofocusing PAGE. The purified enzyme was inhibited by several bivalent cations, such as Cu2+, Fe2+, Hg2+, and by d-glucono-1,5-lactone, showing non-competitive inhibition of the mixed type.
Duroux
L
L
Station d'Amélioration des Arbres Forestiers, I.N.R.A.-Orléans, 45160 Ardon, France.
Delmotte
F M
FM
Lancelin
J M
JM
Kéravis
G
G
Jay-Allemand
C
C
D002384:Catalysis; D005960:Glucosides / Q000737:chemistry* / Q000378:metabolism; D006868:Hydrolysis; D007525:Isoelectric Focusing; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008956:Models, Chemical; D009284:Naphthols / Q000737:chemistry* / Q000378:metabolism; D009285:Naphthoquinones / Q000378:metabolism*; D013379:Substrate Specificity; D001617:beta-Glucosidase / Q000378:metabolism*
D005960:Glucosides; D009284:Naphthols; D009285:Naphthoquinones; C114053:hydrojuglone-beta-D-glucopyranoside; D001617:beta-Glucosidase; C005134:juglone