Tetrahydropterin und Melanophoren-Differenzierung bei Fischen

Abstract

The pterins of adult fishes are located in special chromatophores, the "pterinophores", where they are bound to protein granules. In some cases the centers of these pterinophores also contain droplets of carotenoids. The pterins in the skin of adult fishes are metabolically inactive compounds like xanthopterin, which is shown for 5 different species of Crenilabrus. In the skin of newly hatched Crenilabrus, where melanophore differentiation and intensive melanin synthesis are taking place, instead of xanthopterin a dihydrop-terin and tetrahydropterin are present, both of which were found earlier in insects and amphibians. These pterins are located in bladders within the differentiating melanophores. The tetrahydropterin of animal source acts as a cofactor in enzymatic hydroxylation of phenylalanine to tyrosine (the 1st step in melanin synthesis) in the rat liver system, as was proved by Kaufman for synthetic dimethyltetrahydropterin. These results are discussed in connection with earlier results regarding melanophore development and differentiation.