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The versatility of reactions catalyzed by pyridoxal 5'-phosphate (PLP) enzymes is largely due to the chemistry of their extraordinary catalyst. PLP is necessary for many reactions involving amino acids. Reaction specificity is controlled by the orientation of the external aldimine intermediate that is formed upon addition of the amino acidic substrate to the coenzyme. The breakage of a specific bond of the external aldimine gives rise to a carbanionic intermediate. From this point, the different reaction pathways diverge leading to multiple activities: transamination, decarboxylation, racemization, elimination, and synthesis. A significant novelty appeared approximately 30 years ago when it was reported that some PLP-dependent decarboxylases are able to consume molecular oxygen transforming an amino acid into a carbonyl compound. These side paracatalytic reactions could be particularly relevant for human health, also considering that some of these enzymes are responsible for the synthesis of important neurotransmitters such as γ-aminobutyric acid, dopamine, and serotonin, whose dysregulation under oxidative conditions could have important implications in neurodegenerative states. However, the reactivity of PLP enzymes with dioxygen is not confined to mammals/animals. In fact, some plant PLP decarboxylases have been reported to catalyze oxidative reactions producing carbonyl compounds. Moreover, other recent reports revealed the existence of new oxidase activities catalyzed by new PLP enzymes, MppP, RohP, Ind4, CcbF, PvdN, Cap15, and CuaB. These PLP enzymes belong to the bacterial and fungal kingdoms and are present in organisms synthesizing bioactive compounds. These new PLP activities are not paracatalytic and could only scratch the surface on a wider and unexpected catalytic capability of PLP enzymes.

This was a retrospective pooled analysis of data from four comparably designed, double-blind, placebo-controlled, Phase III studies and their long-term open-label extensions. Patients on levodopa and a dopa decarboxylase inhibitor (DDCI) were randomized to entacapone or to placebo in the 6-month, double-blind phase, with all patients subsequently receiving entacapone in the extension phase. UPDRS III motor scores improved by -2.1 points during the first 6 months of levodopa/DDCI and entacapone therapy, and remained below baseline for up to 2 years. Increased daily 'ON' time, together with response duration to a single morning dose of levodopa and clinical global evaluation, also supported the long-term efficacy of levodopa/DDCI and entacapone. The mean daily dose of levodopa did not increase over the 5-year follow-up period. Long-term therapy with levodopa/DDCI and entacapone was well-tolerated.

Like the adult wing, butterfly larvae are unique in their coloring. However, the molecular mechanisms underlying the formation of insect larval color patterns are largely unknown. The larva of the swallowtail butterfly Papilio xuthus changes its color pattern markedly during the 4th ecdysis. We investigated its cuticular color pattern, which is thought to be composed of melanin and related pigments derived from tyrosine. We cloned three enzymes involved in the melanin-synthesis pathway in P. xuthus: tyrosine hydroxylase (TH), dopa decarboxylase (DDC), and ebony. Whole-mount in situ hybridization showed that the expression of both TH and DDC is strongly correlated with the black markings. ebony is strongly expressed only in the reddish-brown area. The expression pattern of each enzyme coincides with the cuticular color pattern of the subsequent instar. We also investigated the uptake of melanin precursors into cultured integument. Inhibition of either TH or DDC activity prevents in vitro pigmentation completely. Addition of dopamine to integuments in the presence of TH inhibitor causes overall darkening without specific markings. From these results, specific larval cuticular color patterns are regulated by stage-specific colocalization of enzymes in epidermal cells rather than by the differential uptake of melanin precursors into individual epidermal cells. Epidermal cells expressing TH and DDC, but not ebony, produce the black cuticle, and epidermal cells expressing TH, DDC, and ebony produce the reddish-brown cuticle.

During a screening program intended to identify genes encoding enzymes typical for secondary metabolism in Sorangium cellulosum So ce90, an aromatic amino acid decarboxylase gene (ddc) was detected. Expression of ddc in Escherichia coli and subsequent enzyme assays with cell-free extracts confirmed the proposed function derived from amino acid sequence comparisons. In contrast to other aromatic amino acid decarboxylases of eukaryotic origin, the S. cellulosum Ddc converted only L-dihydroxy phenylalanine. This is the first report of a gene encoding an L-dihydroxy phenylalanine decarboxylase in bacteria.

The site of decarboxylation of exogenously administered L-DOPA was studied in corpora striata of rats with near-total unilateral nigrostriatal lesions. After DOPA administration, the absolute increases in dopamine (DA) levels were lower in lesioned than in unlesioned striata, suggesting that, in the intact striatum, a major part of exogenous DOPA is decarboxylated in DA neurons. DOPA can also be decarboxylated outside DA neurons, however, as shown by our finding that relatively higher DOPA decarboxylase than tyrosine hydroxylase activity or DA concentration remains in striata after the nigrostriatal lesions. Also, the percentage increases in DA formation after DOPA administration were much higher in lesioned than in control striata. Rats with both raphé and nigrostriatal lesions failed to exhibit further reductions in striatal DOPA decarboxylase activity or diminished biochemical or behavioral (turning behavior) reactions to DOPA. Inhibition of the DOPA decarboxylase contained in brain capillary endothelial cells did not abolish DA formation in lesioned striata or circling behavior after DOPA administration. These findings all suggest an additional cell type in the striatum as the site of DOPA's decarboxylation in the absence of DA neurons.

An analysis of the presence of catechol-derivatives in the sea anemones Metridium senile and Tealia felina, made with the aid of high-pressure liquid chromatography (HPLC), established the presence of dopa, 5-OH-dopa, and 5-S-cysteinyldopa. In addition, 2-S-cysteinyldopa and 2.5-diSS-cysteinyldopa occurred in Metridium. Two unknown substances were found to be present in the tentacles of Metridium and in the tentacles of some specimens of Tealia. Neither catecholamines nor serotonin could be traced in detectable amounts. No dopa-decarboxylase could be demonstrated by the assay performed in this investigation. 6-OH-dopa, 6-OH-dopamine and reserpine had no effect on the formaldehyde-induced fluorescence of the subepithelial tentacular nerve net of Tealia. It is concluded that the tentacular nerve net of sea anemones contains dopa, but neither catecholamines nor serotonin. The localization of the other compounds is not yet established.

Four monkeys were exposed to a total of 8 g each of manganese as oxide by repetitive subcutaneous injections during 5 months, after which they were left for 1 week to 6 months before they were sacrificed. All animals developed hyperactive behaviour after about 2 months. About 5 months after the start of the exposure the animals became hypoactive with an unsteady gait, and subsequently an action tremor appeared in some of the animals. The animals lost power in both upper and lower limbs and the movements of the hands and feet were very clumsy. The serum content of manganese rose 10-40 times during the exposure time and the content in brain was generally increased more than 10 times, with the highest content found in globus pallidus and putamen. The observed neurochemical effects were also largest in globus pallidus and putamen. In these regions there was a considerable depletion of dopamine and 3,4-dihydroxyphenylacetic acid, while the homovanillic acid content remained almost unchanged. A severe neuronal cell loss was observed in globus pallidus but not in other regions. This is in accordance with results from the most recent neuropathological study of a human suffering from chronic manganese poisoning [Yamada et al. (1986) Acta Neuropathol 70: 273-278] where globus pallidus was devoid of neuronal cells while the content of pigmented cells in substantia nigra was normal. Our data suggest a reduction in number of dopaminergic nerve terminals, as the activity of the dopamine synthesizing enzyme DOPA-decarboxylase was also lowered.(ABSTRACT TRUNCATED AT 250 WORDS)

The cellular localization of the enzymes tyrosine hydroxylase (TH), aromatic amino-acid decarboxylase (or dopa decarboxylase, DDC), dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT) in the adrenal medulla of adult rats and rat fetuses (14th, 17th, 18th, 19th and 21st day) was examined. In the prenatal stages the medullary blastema and an adjacent part of the primitive sympathetic trunk were also investigated. Tissues were fixed in ice-cold 4% paraformaldehyde in 0.1 M phosphate buffer (pH 7.2). Cryostat sections (10 micron in thickness) were stained by the indirect immunofluorescence technique. Rabbit antibodies to TH (isolated from human pheochromocytoma), DDC, DBH and PNMT (the latter three isolated from bovine adrenal medulla) were used. Sections incubated with serum of non-immunized rabbits were used as controls. In the adult adrenal medulla, two cell types can be distinguished. One cell type contains only TH, DDC and DBH. The other cell type contains PNMT in addition. It is concluded that these cells correspond to the noradrenaline-(NA-) and adrenaline- (A-)storing cells respectively. In all prenatal stages TH, DDC and DBH are found in the primitive sympathetic trunk, in the medullary blastema, and in the medullary cells which have migrated into the cortical "anlage". PNMT is observed for the first time on the 18th day. Moreover, PNMT could only be demonstrated inside the adrenal gland. From these observations it is concluded that the capacity to synthesize NA is developed even before the "medullary" cells have reached the cortical "anlage". On the contrary, the capacity to synthesize A seems to be acquired only after this contact is established. The hypothesis is put forward that this phenomenon might indicate the induction of PNMT by glucocorticoids secreted by the fetal cortex.

Experiments involving combined injections of a drogue (Ro4-4602 or nialmide) and precursor (3H-5-HTP) allowed to determine the best conditions for performing an experimental study of serotonin (5-HT) synthesis and metabolism in the embryonic pineal organ of Lacerta vivipara. Inhibition of 5-HT synthesis at the decarboxylation step using Ro4-4602 significantly reduces the tritiated indolamine rates in the pineal sensory epithelium of embryos of the stages 37-40. In contrast with the embryos of stages 36 to 40 which received injections of 3H-5-HTP only, the secretory rudimentary photoreceptor cells (SRP) of embryos of the same stages which were pretreated with Ro4-4602 do not show a selective radioautographic labeling. After inhibition of the monoamine oxidases with nialomide, the tritiated indolamine rates are significantly increased in the SRP of embryos of stages 35 to 40. Our radioautographic studies show indirectly the early presence of 5-HTPD and MAO in the SRP (stage 35) during the pineal embryogenesis of Lacerta. In the distal part of the pineal, monoamine oxidase activity is histochemically demonstrated at stage 34. During ontogenesis, the reaction becomes increasingly intensive in the apical part of the epithelial cells while it extends to the epithelium of the proximal part of the pineal organ.

Crude synaptosomal preparations of rat brain were separated by concomitant flotation and sedimentation in a sucrose gradient into fractions containing myelin, nerve endings, and mitochondria, respectively. Two myelin-free nerve ending fractions were obtained which differ in the serotonin content and the activities of the enzymes 5-hydroxytryptophan decarboxylase, monoamine oxidase, choline acetylase, and acetylcholin-esterase. In glucose medium sodium ions stimulate serotonin uptake into the nerve endings while potassium ions in sucrose solution induce the release of this amine.