[Incontinentia pigmenti: a case study]. / Incontinentia pigmenti: à propos d'un cas.

Incontinentia pigmenti is a rare hereditary, dominant, X-linked disorder. It involves the skin, the teeth, the eyes and the central nervous system. The case we report is an infant girl aged 2 months. She had typical skin lesions associated with severe impairment of her left eye. We comment on the clinical, histological, genetic, and therapeutic characteristics of this rare disease. Ophthalmologic examination should be made early in order to diagnose ocular involvement at an early stage of the disease to provide for greater treatment possibilities.

[Rat bite: an unusual cause of orbital cellulitis]. / Morsure par un rat: une cause inhabituelle de cellulite orbitaire.

Rat bite is rarely reported in the literature. We report the case of a 33-year-old woman who was bitten by a rat on her upper eyelid. The clinical examination showed a large palpebral edema extending to the side of the face, associated with local signs of inflammation. Visual acuity was preserved and tomodensitometry showed a small exophthalmia that did not extend to the sinuses. This lesion led to a diagnosis of orbital cellulitis. Progression was favorable with antibiotics: amoxicillin, clavulanic acid, gentamicin, and metronidazole. The authors discuss the compromised prognosis of this disease and the necessity of rapid diagnosis and prompt therapeutic management.

Mechanistic studies on tyrosinase-catalysed oxidative decarboxylation of 3,4-dihydroxymandelic acid.

Mushroom tyrosinase, which is known to convert a variety of o-diphenols into o-benzoquinones, has been shown to catalyse an unusual oxidative decarboxylation of 3,4-dihydroxymandelic acid to 3,4-dihydroxybenzaldehyde [Sugumaran (1986) Biochemistry 25, 4489-4492]. The mechanism of this reaction was re-investigated. Although visible-region spectral studies of the reaction mixture containing 3,4-dihydroxymandelic acid and tyrosinase failed to generate the spectrum of a quinone product during the steady state of the reaction, both trapping experiments and non-steady-state kinetic experiments provided evidence for the transient formation of unstable 3,4-mandeloquinone in the reaction mixture. The visible-region spectrum of mandeloquinone resembled related quinones and exhibited an absorbance maximum at 394 nm. Since attempts to trap the second intermediate, namely alpha,2-dihydroxy-p-quinone methide, were in vain, mechanistic studies were undertaken to provide evidence for its participation. The decarboxylative quinone methide formation from 3,4-mandeloquinone dictates the retention of a proton on the alpha-carbon atom. Hence, if we replace this proton with deuterium, the resultant 3,4-dihydroxybenzaldehyde should retain the deuterium present in the original substrate. To test this hypothesis, we chemoenzymically synthesized alpha-deuterated 3,4-dihydroxymandelic acid and examined its enzymic oxidation. Our studies reveal that the resultant 3,4-dihydroxybenzaldehyde retained nearly 90% of the deuterium, strongly indicating the transient formation of quinone methide. On the basis of these findings it is concluded that the enzymic oxidation of 3,4-dihydroxymandelic acid generates the conventional quinone product, which, owing to its unstability, is rapidly decarboxylated to generate transient alpha,2-dihydroxy-p-quinone methide. The coupled dienone-phenol re-arrangement and keto-enol tautomerism of this quinone methide produce the observed 3,4-dihydroxybenzaldehyde.

The mechanism of tyrosinase-catalysed oxidative decarboxylation of alpha-(3,4-dihydroxyphenyl)-lactic acid.

Mushroom tyrosinase, which is known to catalyse the conversion of o-diphenols into o-benzoquinones, has been shown to catalyse the oxidative decarboxylation of 3,4-dihydroxymandelic acid [Sugumaran (1986) Biochemistry 25, 4489-4492]. To account for this unusual reaction, a quinone methide intermediate has been proposed. Since all attempts to trap this intermediate ended in vain, mechanistic studies were designed to support the formation of this transient product. Replacement of the alpha-proton in 3,4-dihydroxymandelic acid with a methyl group generates alpha-(3,4-dihydroxyphenyl)-lactic acid, the enzymic oxidation of which should produce 3,4-dihydroxyacetophenone as the end product if the oxidative decarboxylation proceeds through the quinone methide intermediate. Accordingly, chemically synthesized alpha-(3,4-dihydroxyphenyl)-lactic acid on enzymic oxidation produced 3,4-dihydroxyacetophenone as the major isolatable product. Non-steady-state kinetic analysis of the enzyme reaction attested to the transient formation of the conventional quinone product. Thus the enzymic oxidation of alpha-(3,4-dihydroxyphenyl)-lactic acid seems to generate the conventional quinone, which, owing to its instability, is rapidly decarboxylated to yield the transient quinone methide. The coupled dieneonephenol re-arrangement and ketol-enol tautomerism transforms the quinone methide into 3,4-dihydroxyacetophenone.

Oxidation of 3,4-dihydroxybenzyl alcohol: a sclerotizing precursor for cockroach ootheca.

The oxidation of 3,4-dihydroxybenzyl alcohol, one of the sclerotizing precursors for the tanning of the ootheca of cockroach Periplaneta americana, is reported for the first time. Mushroom tyrosinase catalyzed oxidation of 3,4-dihydroxybenzyl alcohol generated the corresponding quinone which was found to be unstable and readily transformed to produce 3,4-dihydroxybenzaldehyde as the stable product probably through the intermediary formation of a quinone methide. Phenoloxidase isolated from the left collateral gland of P. americana also catalyzed this new reaction. When the enzymatic oxidation of 3,4-dihydroxybenzyl alcohol was performed in the presence of a test protein such as lysozyme, the reactive species formed, caused the oligomerization of test protein. Similar studies with collateral gland proteins, failed to generate oligomers, but produced insoluble polymeric proteins. The probable fate of 3,4-dihydroxybenzyl alcohol for the tanning of cockroach ootheca is discussed.

Quinone and quinone methide as transient intermediates involved in the side chain hydroxylation of N-acyldopamine derivatives by soluble enzymes from Manduca sexta cuticle.

Proteins solubilized from the pharate cuticle of Manduca sexta were fractionated by ammonium sulfate precipitation and activated by the endogenous enzymes. The activated fraction readily converted exogenously supplied N-acetyldopamine (NADA) to N-acetylnorepinephrine (NANE). Either heat treatment (70 degrees C for 10 min) or addition of phenylthiourea (2.5 microM) caused total inhibition of the side chain hydroxylation. If chemically prepared NADA quinone was supplied instead of NADA to the enzyme solution containing phenylthiourea, it was converted to NANE. Presence of a quinone trap such as N-acetylcysteine in the NADA-cuticular enzyme reaction not only prevented the accumulation of NADA quinone, but also abolished NANE production. In such reaction mixtures, the formation of a new compound characterized as NADA-quinone-N-acetylcysteine adduct could be readily witnessed. These studies indicate that NADA quinone is an intermediate during the side chain hydroxylation of NADA by Manduca cuticular enzyme(s). Since such a conversion calls for the isomerization of NADA quinone to NADA quinone methide and subsequent hydration of NADA quinone methide, attempts were also made to trap the latter compound by performing the enzymatic reaction in methanol. These attempts resulted in the isolation of beta-methoxy NADA (NADA quinone methide methanol adduct) as an additional product. Similarly, when the N-beta-alanyldopamine (NBAD)-Manduca enzyme reaction was carried out in the presence of L-kynurenine, two diastereoisomers of NBAD quinone methide-kynurenine adduct (= papiliochrome IIa and IIb) could be isolated.(ABSTRACT TRUNCATED AT 250 WORDS)

On the mechanism of side chain oxidation of N-beta-alanyldopamine by cuticular enzymes from Sarcophaga bullata.

The metabolism of N-beta-alanyldopamine (NBAD) by Sarcophaga bullata was investigated. Incubation of NBAD with larval cuticular preparations resulted in the covalent bindings of NBAD to the cuticle and generation of N-beta-alanyl-norepinephrine (NBANE) as the soluble product. When the reaction was carried out in presence of a powerful quinone trap viz., N-acetylcysteine, NBANE formation was totally abolished; but a new compound characterized as NBAD-quinone-N-acetylcysteine adduct was generated. These results indicate that NBAD quinone is an obligatory intermediate for the biosynthesis of NBANE in sarcophagid cuticle. Accordingly, phenylthiourea--a well-known phenoloxidase inhibitor--completely inhibited the NBANE production even at 5 microM level. A soluble enzyme isolated from cuticle converted exogenously supplied NBAD quinone to NBANE. Chemical considerations indicated that the enzyme is an isomerase and is converting NBAD quinone to its quinone methide which was rapidly and nonenzymatically hydrated to form NBANE. Consistent with this hypothesis is the finding that NBAD quinone methide can be trapped as beta-methoxy NBAD by performing the enzymatic reaction in 10% methanol. Moreover, when the reaction was carried out in presence of kynurenine, two diastereoisomeric structures of papiliochrome II-(Nar-[alpha-3-aminopropionyl amino methyl-3,4-dihydroxybenzyl]-L-kynurenine) could be isolated as by-products, indicating that the further reactions of NBAD quinone methide with exogenously added nucleophiles are nonenzymatic and nonstereoselective. Based on these results, it is concluded that NBAD is metabolized via NBAD quinone and NBAD quinone methide by the action of phenoloxidase and quinone isomerase respectively. The resultant NBAD quinone methide, being highly reactive, undergoes nonenzymatic and nonstereoselective Michael-1,6-addition reaction with either water (to form NBANE) or other nucleophiles in cuticle to account for the proposed quinone methide sclerotization.

Mechanism of activation of 1,2-dehydro-N-acetyldopamine for cuticular sclerotization.

The mechanism of oxidation of 1,2-dehydro-N-acetyldopamine (dehydro NADA) was examined to resolve the controversy between our group and Andersen's group regarding the reactive species involved in beta-sclerotization. While Andersen has indicated that dehydro NADA quinone is the beta-sclerotizing agent [Andersen, 1989], we have proposed quinone methides as the reactive species for this process [Sugumaran, 1987; Sugumaran, 1988]. Since dehydro NADA quinone has not been isolated or identified till to date, we studied the enzymatic oxidation of dehydro NADA in the presence of quinone traps to characterize this intermediate. Accordingly, both N-acetylcysteine and o-phenylenediamine readily trapped the transiently formed dehydro NADA quinone as quinone adducts. Interestingly, when the enzymatic oxidation was performed in the presence of o-aminophenol or different catechols, adduct formation between the dehydro NADA side chain and the additives had occurred. The structure of the adducts is in conformity with the generation and reactions of dehydro NADA quinone methide (or its radical). This, coupled with the fact that 4-hydroxyl or amino-substituted quinones instantly transformed into p-quinonoid structure, indicates that dehydro NADA quinone is only a transient intermediate and that it is the dehydro NADA quinone methide that is the thermodynamically stable product. However, since this compound is chemically more reactive due to the presence of both quinone methide and acylimine structure on it, the two side chain carbon atoms are "activated." Based on these considerations, it is suggested that the quinone methide derived from dehydro NADA is the reactive species responsible for cross-link formation between dehydro NADA and cuticular components during beta-sclerotization.

Nonenzymatic transformations of enzymatically generated N-acetyldopamine quinone and isomeric dihydrocaffeiyl methyl amide quinone.

We have recently demonstrated that the side chain hydroxylation of N-acetyldopamine and related compounds observed in several insects is caused by a two-enzyme system catalyzing the initial oxidation of catecholamine derivatives and subsequent isomerization of the resultant quinones to isomeric quinone methides, which undergo rapid nonenzymatic hydration to yield the observed products [Saul, S.J. and Sugumaran, M. (1989) FEBS Lett. 249, 155-158]. During our studies on o-quinone/p-quinone methide tautomerase, we observed that quinone methides are also produced nonenzymatically slowly, under physiological conditions. The quinone methide derived from N-acetyldopamine was hydrated to yield N-acetylnorepinephrine as the stable product as originally shown by Senoh and Witkop [(1959) J. Am. Chem. Soc. 81, 6222-6231], while the isomeric quinone methide from dihydrocaffeiyl methylamide exhibited a new reaction to form caffeiyl amide as the stable product. The identity of this product was established by UV and IR spectral studies and by chemical synthesis. We could not find any evidence of intramolecular cyclization of N-acetyldopamine quinone to iminochrome-type compound(s). The importance of quinone methides in these reactions is discussed.

Tyrosinase-catalyzed unusual oxidative dimerization of 1,2-dehydro-N-acetyldopamine.

Tyrosinase, which usually catalyzes the conversion of o-diphenols to o-benzoquinones, catalyzed an unusual oxidative dimerization of 1,2-dehydro-N-acetyl-dopamine to a benzodioxan derivative. The identity of the product was confirmed by UV, IR spectra, and NMR studies. During the oxidation, generation of a transient reactive intermediate could be witnessed by its characteristic visible absorption spectrum. Typical phenoloxidase inhibitors such as phenylthiourea, potassium cyanide, sodium azide, and sodium fluoride drastically inhibited the above reaction. Mimosine, a known competitive inhibitor of o-diphenoloxidase activity, also inhibited the new reaction competitively, suggesting that both the observed oxidative dimerization and the conventional quinone production are catalyzed by the same active site copper of tyrosinase. Based on our earlier findings (Sugumaran, M., and Lipke, H. (1983) FEBS Lett. 155, 65-68; Sugumaran, M. (1986) Biochemistry 25, 4489-4492) that phenoloxidases can produce quinone methides from certain 4-alkylcatechols, possible mechanisms for this new reaction are presented.

Duodenal ulcer induced by MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine).

Experiments in rats revealed that the parkinsonian drug 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) given in multiple daily doses either per os (p.o.) or subcutaneously (s.c.) induced in a dose-dependent manner solitary or double ("kissing") duodenal ulcers in the rat. MPTP also diminished cerebral concentrations of DOPAC and the duodenal ulcers were prevented by pretreatment with dopamine agonists (e.g., bromocriptine, lergotrile) or monoamine oxidase inhibitors (e.g., pargyline, 1-deprenyl). High doses of MPTP also caused gastric erosions and motility changes resembling parkinsonism (e.g., akinesia, rigidity, forward bending of trunk). This chemical decreased gastric secretion of acid and pepsin, as well as pancreatic bicarbonate, trypsin and amylase. Thus, MPTP causes duodenal ulcers that are possibly associated with impaired defense in the duodenal bulb (e.g., decreased availability of duodenal and pancreatic bicarbonate).