The nature of the pigment formed by Vibrio cholerae and the characterization of its biosynthetic pathway is shown. This microorganism is able to synthesize melanin-like pigment when cultured in the presence of L-tyrosine. Other phenolic chemicals related to L-tyrosine do not lead to pigment production. The microorganism has no tyrosine hydroxylase activity, and the levels of dopa oxidase activity are very low, making the existence of a tyrosinase very unlikely. However, Vibrio cholerae contained transaminases that transforms L-tyrosine into p-hydroxyphenylpyruvate. Moreover, Vibrio cholerae is able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously be oxidized to its p-quinone form, which subsequently polymerizes leading to pigment formation. It is concluded that the pigment formed by Vibrio cholerae is not synthesized by the Raper-Mason pathway, but by a L-tyrosine catabolism pathway leading to homogentisic acid. Some simple properties of that melanin are compared to model eu- and pheomelanin, but no clear distinction could be stated, indicating the similarity between all these pigments.

The aminoacyl-imidazole dipeptides carnosine (beta-alanyl-L-histidine) and anserine (beta-alanyl-1-methyl-histidine) are present in relatively high concentrations in excitable tissues, such as muscle and nervous tissue. In the present study we describe the existence of a marked sexual dimorphism of carnosine and anserine in skeletal muscles of CD1 mice. In adult animals the concentrations of anserine were higher than those of carnosine in all skeletal muscles studied, and the content of aminoacyl-imidazole dipeptides was remarkably higher in males than in females. Postnatal ontogenic studies and hormonal manipulations indicated that carnosine synthesis was up-regulated by testosterone whereas anserine synthesis increased with age. Regional variations in the concentrations of the dipeptides were observed in both sexes, skeletal muscles from hind legs having higher amounts of carnosine and anserine than those present in fore legs or in the pectoral region. The concentration of L-lysine in skeletal muscles also showed regional variations and a sexual dimorphic pattern with females having higher levels than males in all muscles studied. The results suggest that these differences may be related with the anabolic action of androgens on skeletal muscle.

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The identity of the product of the meL4 gene from Shewanella colwelliana with the enzyme p-hydroxyphenylpyruvic dioxygenase is shown. Cloning of the melA gene endowed Escherichia coli with the capacity to synthesize melanin-like pigments from L-tyrosine. E. coli contained transaminases that transforms L-tyrosine into p-hydroxyphenylpyruvate. This keto acid was detected in the cultures. On the other hand, E. coli containing melA was able to go further in the catabolic pathway, releasing a great amount of homogentisic acid. This acid can spontaneously polymerize giving the pigment. Furthermore, p-hydroxyphenylpyruvate dioxygenase activity was detected in this system. Analysis of the deduced amino acid sequence revealed a high homology with the p-hydroxyphenylpyruvate dioxygenase enzyme from different organisms.

Feeding mice an arginine-deficient diet decreased plasma concentrations of arginine, citrulline and ornithine in the females and arginine in the males, abolishing the sexual dimorphic pattern of these amino acids found in mice fed the standard diet. In addition, the restriction of dietary arginine produced a marked decrease in body and renal weights as well as in the activity of renal ornithine decarboxylase, decreases that were gender dependent since they were observed exclusively in males. The fact that these changes were not associated with the decrease in the circulating levels of testosterone and that the dietary arginine restriction prevented the body weight gain induced by testosterone treatment of female mice fed the standard diet indicates that dietary arginine is required for the anabolic action of androgens. Moreover, under certain conditions that could compromise the renal synthesis of arginine, as in the compensatory renal hypertrophy that follows unilateral nephrectomy, the myotrophic effect of testosterone was transiently impaired. The results also revealed that arginine deficiency produced an opposite effect in the expression of IGF-I and IGF-binding protein 1 in the liver and kidney. Taken together, our results indicate that dietary arginine may be relevant to the anabolic action of testosterone, and suggest that this effect may be mediated by changes in the insulin-like growth factor system.