Untersuchungen zur synthese und zum metabolismus von aminosäuren in larven des wildtyps und der letalmutanten l(3)tr und l(2)me von Drosophila melanogaster

Abstract

Free and protein-bound amino-acids of Drosophila melanogaster larvae of the wild type and the lethal mutants, l(3)tr and l(2)me, reared aseptically on a semi-defined medium have been studied. The contents of free, ninhydrin-positive components are closely related to fresh weights. Compared to larvae reared on standard medium those raised under sterile conditions have a lower protein content, particularly the genotype lme. Molar concentrations of free amino-acids are higher in ltr- larvae than in the wild-type. To a lesser extent the same is true for protein-bound amino-acids. By contrast, there is a reduction of the amino-acid concentration in lme- larvae , with the exception of free glycine, whereby the free amino-acids are more affected than the protein-bound ones. The relative pattern of free amino-acids is specific for each genotype. There is an accumulation of glutamine and lysine in ltr and glycine and threonine in lme. On the other hand, the amino-acid patterns in protein hydrolysates are similar for all three genotypes. After feeding the larvae with [ 14C]glucose the following amino-acids were found to belabelled in all three genotypes: α-alanine, aspartic acid, glutamic acid, glycine, proline, serine, threonine, glutamine, and an unknown substance (U 3). In addition, tyrosine and phenylalanine were radioactive in the wild type, β-alanine, tyrosine, and valine in ltr and arginine/histidine, asparagine, leucine/isoleucine, and valine in lme. The relative distribution of radioactivity varies with free and protein-bound amino-acids as well as with the genotypes. The specific activities show that the relative rate of amino-acid synthesis from glucose depends on the genotype. Furthermore, differences in specific activities between free and protein-bound amino-acids have been observed, indicating that the free amino-acid pool does not represent the pool available to protein synthesis. In contrast to the generally accepted view, glycine and threonine are synthesized to such an extent that they should not be designated as essential for Drosophila melanogaster. There are also indications from the present study that phenylalanine, valine, leucine/isoleucine, and arginine/histidine may probably be non-essential too.