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Basic and Neutral Amino Acid Transport in Aspergillus nidulans
Abstract
Summary: Arginine and methionine transport by Aspergillus nidulans mycelium was investigated.
A single uptake system is responsible for the transport of arginine, lysine and ornithine. Transport is energy-dependent and specific for these basic amino acids. The K m value for arginine is 1 × 10−5 m, and V max is 2·8 nmol/mg dry wt/min; K m for lysine is 8 × 10−6 m; K i for lysine as inhibitor of arginine uptake is 12 μ m, and K i for ornithine is 3 mm.
On minimal medium, methionine is transported with a K m of 0·1 mm and V max about 1 nmol/mg dry wt/min; transport is inhibited by azide. Neutral amino acids such as serine, phenylalanine and leucine are probably transported by the same system, as indicated by their inhibition of methionine uptake and the existence of a mutant specifically impaired in their transport.
The recessive mutant nap3, unable to transport neutral amino acids, was isolated as resistant to selenomethionine and p-fluorophenylanine. This mutant has unchanged transport of methionine by general and specific sulphur-regulated permeases.
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© Society for General Microbiology 1976