Effect of NAD(P)H:quinone oxidoreductase on tyrosinase-mediated oxidation of opioid neuropeptides Leu-enkephalin and Met-enkephalin.

In vitro experiments are reported showing that NAD(P)H:(quinone acceptor) oxidoreductase (QR), purified from Glycine max seedlings, reduces Leu- and Met-enkephalin-tyrosinase oxidation products, in the presence of NADH or NADPH. QR was not capable to catalyze the reduction of N-acetyl-dopaquinone formed by the cation of mushroom tyrosinase on N-acetyl-L-tyrosine, while it was able to reduce dopachrome. The results support the hypothesis that QR can inhibit the formation of melanin-like compounds, as catalyzed by the action of tyrosinase on Leu-enkephalin and Met-enkephalin. It is proposed that, in the presence of NAD(P)H as the electron donor, the inhibition occurs by the specific conversion of the dopachrome-derivative into the reduced precursor, leucodopachrome-derivative.

Autoxidation of 4-methylcatechol: a model for the study of the biosynthesis of copper amine oxidases quinonoid cofactor.

The autoxidation of 4-methylcatechol under quasi-physiological conditions, leading to 2-hydroxy-5-methyl-1,4-benzoquinone, was investigated. The effects of pH and metal ions were examined. An electrophilic attack of dioxygen to the 4-methylcatechol monoanion to form a transient peroxo species is proposed. It was concluded that such a non-enzymic conversion is likely for this model compound and for its physiological counterpart, a specific tyrosyl residue incorporated in the protein chain at the active site of copper amine oxidases.

A hydroxyquinone with amine oxidase activity: preparation and properties.

The preparation and some properties of a hydroxyquinone showing an amine oxidase-like activity are described. The compound, 2-hydroxy-5-methyl-1,4-benzoquinone, oxidizes a wide range of primary amines, both benzylic and non-benzylic, at the expenses of molecular oxygen in the presence of Cu2+ ions, and reacts with hydrazine derivatives leading to stable, inactive adducts. This behaviour is similar to that of 2,4,5-trihydroxyphenylalanine quinone-containing amine oxidases and therefore the present compound could be a useful model to understand the reaction mechanism of those enzymes.

Purification and characterization of an NAD(P)H:quinone oxidoreductase from Glycine max seedlings.

An NAD(P)H:(quinone acceptor) oxidoreductase (EC 1.6.99.2) was purified from Glycine max seedlings by means of chromatographic procedures. After 1371-fold purification, the enzyme showed a single band in IEF corresponding to an isoelectric point of 6.1. A single band was also found in native-PAGE both by activity staining and Coomassie brilliant blue staining. The molecular mass determined in SDS-PAGE was 21900 Da, while in HPLC gel-filtration it was 61000 Da. The NAD(P)H:quinone oxidoreductase was able to use NADH or NADPH as the electron donor. Among the artificial quinones which are reduced by this enzyme, 6-hydroxydopa- and 6-hydroxydopamine-quinone are of particular interest because of their neurotoxic effects.

Repeated albumin infusions do not lower blood pressure in preeclampsia.

Since intravascular volume contraction is regarded as an important pathological feature in preeclampsia, it has been proposed that plasma volume expansion could be a therapeutic manoeuver that interrupts the pathogenetic chain of hypovolemia inducing increased vascular resistance. Furthermore, tissue perfusion should be improved and, if albumin is used as plasma expander agent, interstitial edema should also be reduced. We report the results observed in an open pilot study in ten preeclamptic patients treated with daily albumin infusions (0.4 to 1 g/kg) from 7 to 36 days. No acute effects were shown on blood pressure, and the need for antihypertensive therapies did not decrease in the following days. Serial evaluation after at least five or ten days of repeated albumin infusions did not show stable changes in electrolytes excretion, renal clearances, serum protein concentration and hematocrit value, nor in aldosterone, renin and atrial natriuretic peptide basal levels, while proteinuria tended to increase. Uteroplacental and fetoplacental blood flow acutely ameliorated in 3 cases only after albumin 1 g/Kg, but reached basal values again on the next day. The clinical implications are that daily albumin infusions with this schedule dosage do not lower blood pressure and that they are unable to induce stable changes in renal function, uteroplacental and fetoplacental resistance. No maternal complications were observed during the conservative management, but fetal mortality was high (6/10). Given the uncontrolled study, we cannot know whether similar results had been achieved by conventional therapy only.