Uptake and incorporation of amino acids in minute mutants of Drosophila

Abstract

Uptake into blood and incorporation into tissue protein of cystine-3% were assayed in larvae of controls and of five heterozygous Minute mutants of Drosophila melanogaster. The mutants studied were M(2)S-10, M(2)1*, M(2)z, M(3)y and M(3)w. In all mutants, the level of cystine in the blood was significantly higher than in controls and differences in concentration between these mutants were evident. All mutants incorporated cystine into protein, although the specific activities obtained were dependent on genotype. The fraction of the cystine in the blood pool which was incorporated into protein was directly correlated with viability and rate of growth. In contrast, the radioactivity of leucine-l-14C, both in blood and in tissue proteins, was not different in M(2)12 and M(3)w heterozygotes as compared to controls, although in M(2)12 the fraction of leucine in the blood pool incorporated into protein was lowered. It was concluded that these mutants possessed a common inability to withdraw cystine (or other sulfur-containing compounds) from the blood into various metabolic pathways. Feeding activity, digestion and absorption of nutrients appeared normal in these mutants.