We describe results demonstrating the positive regulation of melanogenesis by two substrates of the melanogenic pathway. We have found that L-tyrosine and L-dihydroxyphenylalanine (L-dopa), whose metabolic fates are affected by the activity of that pathway, can also act as its regulators. In living pigment cells, tyrosinase (EC 1.14.18.1), a crucial and rate-limiting enzyme of melanogenesis, ac...

Dopamine replacement therapy for Parkinson’s disease is achieved using L-DOPA or dopamine D2/3 agonists, such as ropinirole. Here, we compare the effects of and ropinirole, alone in combination, on patterns glial microvascular reactivity striatum. Rats with unilateral 6-hydroxydopamine lesions were treated therapeutic-like doses (6 mg/kg), an equipotent L-DOPA-ropinirole combination (L-DOPA 3 m...

Dihydroxyphenylalanine (DOPA) is a neutral amino acid that resembles natural L-dopa (dopamine precursor). It enters the catecholamine metabolic pathway of endogenous L-DOPA in the brain and peripheral tissues. It is amenable to labeling with fluorine-18(F) for PET imaging and was originally used in patients with Parkinson's disease to assess the integrity of the striatal dopaminergic system. Th...

The activity of extracellular phenol oxidases is believed to play a critical role in decomposition processes in peatlands. The water logged, acidic conditions, and recalcitrant litter from the peatland vegetation, lead to exceptionally high phenolics in the peat. In order to quantify the activity of oxidative enzymes involved in the modification and break down of phenolic compounds two types of...

The eastern tiger swallowtail butterfly Papilio glaucus shows a striking example of Batesian mimicry. In this species, females are either wild type (yellow and black) or melanic (where most of the yellow colour is replaced by black). In order to understand how these different colour patterns are regulated, we examined the temporal order of wing pigment synthesis via precursor incorporation stud...

We have investigated the effect of precociously increasing locomotor activity during early postnatal development by daily treatment with the monoaminergic precursor L-DOPA on the survival of motoneurones supplying the slow soleus (SOL) muscle and the fast, tibialis anterior (TA) and extensor digitorum longus (EDL) muscles as well as the contractile and histochemical properties of these muscles....

The aim of the present study was to investigate the possibility that catecholaminergic pathways within the central nervous system play a role in the control of renin secretion. Plasma renin activity (PRA) was measured after intravenous administration of L-dopa with and without prior inhibition of extracerebral dopa decarboxylase by carbidopa (MK-486) in pentobarbital-anesthetized dogs in which ...

In a previous investigation of tyrosinase activity in the cells of the nucleus substantiae nigrae of adult cats and monkeys, diphenolase, but not monophenolase activity, was detected. This is possibly due to inhibition of monophenolase. When the copper radicle in tyrosinase is oxidized, monophenolase cannot be detected, but reducing agents activate and unmask this component of tyrosinase. The e...

Melanoma risk is 30 times higher in people with lightly pigmented skin compared to those darkly skin. Here we show that this difference results from more than melanin pigment and its associated ultraviolet radiation (UVR) shielding effect. Using primary human melanocytes representing the full continuum several preclinical melanoma models, cell-intrinsic differences between dark light regulate m...