Tyrosinase-produced quinones and the disappearance of kynurenine in larval extracts of Drosophila melanogaster

The chemical interaction between adrenochrome, three different classes of antipsychotic drugs and metabolites of the kynurenine pathway

Two kynurenine metabolites, 3-hydroxykynurenine and 3-hydroxyanthranilic acid, are known to inhibit melanin polymer formation in in vitro reactions catalyzed by tyrosinase. The present study expands that finding to include inhibition of chlorpromazine-stimulated melanin formation from the endogenous melanin precursor adrenochrome. Several kynurenine pathway metabolites tested had no measurable effect on the reaction: tryptophan, kynurenine, kynurenic acid, quinolinic acid and nicotinic acid. However, at a concentration of 0.5mM in a pH 7.4 reaction mix, 3-hydroxykynurenine exerted~72% inhibition on product formation and the same concentration of 3-hydroxyanthranilic acid caused complete inhibition. Two other classes of antipsychotic drugs were evaluated in this paradigm, represented by olanzapine and minocycline. Although the adrenochrome reaction of both drugs was strongly inhibited by 3-hydroxyanthranilic acid, 3-hydroxykynurenine inhibited product formation from only the minocycline reaction. The results are discussed in terms of the well-studied kynurenine pathway upregulation in psychotic disorders and how such upregulation may either influence the efficacy of antipsychotic drug treatment or relate to the mechanism of action of these drugs.

An inducible enzyme system in the larval cells of Drosophila melanogaster

An adaptive increase in tryptophan pyrrolase activity was obtained in the cell-free extracts of Drosophila melanogaster larvae which were given a dietary supplement of L-tryptophan. This activity was detectable in the extracts prepared from larval fatbodies when these were isolated from the remaining body tissues, but the present methods did not reveal any activity in extracts from the latter. These experiments confirm previous observations on the cellular distribution of kynurenine after feeding experiments with tryptophan. The autofluorescence characteristic of kynurenine in the larval fatbody is limited to the cells of the anterior region under normal feeding conditions, but, when larvae are fed tryptophan, autofluorescent kynurenine globules are found in a larger number of fat cells. In vitro incubation of isolated posterior fat cells with tryptophan has shown that these cells are capable of producing kynurenine. It is this same region of the fatbody in the suppressor of vermilion mutant that develops kynurenine autofluorescence, thus indicating that the absence of kynurenine in these cells in the normal strain is the result of an inhibition of their genetic potential to produce kynurenine. It has been concluded that the differentiation of "kynurenine cells" in the fatbody is controlled by a genetic mechanism which operates through the inducible tryptophan pyrrolase system.

The dark brown integumentary pigment of a barnacle (Balanus eburneus). A comparative study

A histochemical analysis involving tinctorial and solubility tests was pursued in conjunction with electron microscopy for the purpose of identifying the dark brown epidermal pigment of a barnacle (Balanus eburneus) as melanin and/or ommochrome. Histochemically, comparisons were made with other brown pigments located in the subcarapal epidermis of another crustacean, the fiddler crab (Uca pugilator), the dorsal skin of the red-backed salamander (Plethodon cinereus), the liver and testis of a slider turtle (Chrysemys sp.) and the substantia nigra of human brain. The solubility properties of the pigment of the two crustacean invertebrates were in general similar to one another and markedly different from the pigment of the three vertebrates. Insolubility in appropriate solvents classified the vertebrate pigment as melanin. The invertebrate pigment, however, which was soluble in the ommochrome solvents, concentrated sulfuric and formic acids and 2-chloroethanol, remained insoluble in the ommochrome solvents, dilute aqueous and methanolic hydrochloric acid and dilute sulfuric acid. On the basis of these solubilities, an unequivocal classification of the invertebrate pigment as either melanin or ommochrome did not appear possible. The tinctorial and electron microscopic properties of the barnacle pigment were also equally ambiguous in regard to its specific classification.