Interactions Between Amino Acid Transport Systems in Neurospora crassa

Abstract

Mutants of Neurospora crassa, selectesi as resistant to L-canavanine and Lthialysine, are partially deficient in the uptake of basic amino acids. Neutral amino acids completely inhibit uptake of basic amino acids, and this inhibition is dependent on the activity of a neutral amino acid permease. In contradistinction, mutants resistant to 4-methyl-DL-tryptophan are partially deficient in the uptake of neutral amino acids. Basic amino acids completely inhibit neutral amino acid uptake, and this inhibition is dependent on the activity of a basic amino acid permease. It is proposed that these specific transport systems compete with a general amino acid permease for some common element. The general permease is also regulated by ammonia, the amino acid pool, or both. The activity of the general permease can be eliminated phenotypically by a high concentration of glycerol or a high temperature. It is also shown that Lcitrulline is transported by the neutral amino acid permease and by the general amino acid permease.

Biochemical genetics of Neurospora crassa conidial germination.

“…Many mutant strains have been isolated that have defective or altered transport of either neutral (87,91,107,111,148,160,190,232) or basic (28,111,148,153,160,205,232,237) amino acids. No mutant strains have been reported with defective general or acidic amino acid transport systems.…”

Influence of exogenous sugars and polyols on C1-influx and efflux by the ascomycete Neocosmospora vasinfecta

“…Sanchez et al (22) showed that there was interaction between neutral and basic amino acid transport by Neurospora crassa even though separate permeases were involved. All these authors have suggested that interaction between fluxes of dissimilar compounds may be mediated by competition for some common element such as an energy-coupling mechanism in the cell membrane (8,9,20,22). Such an explanation may hold for the interaction of Cl-and carbohydrate transport by Neocosmospora as both the accumulation of Cl-and glucose by the mycelium appear to be energy-demanding processes (18; Budd, manuscript in preparation).…”

Effects of ribonuclease A on amino acid transport in Neurospora crassa

“…Present data indicate that the G system is inhibited at lower concentrations of enzyme than the N system of phenylalanine transport. It has been reported that a high concentration of glycerol will eliminate the activity of the general permease (14). It has also been reported that extraction of conidia with 4.8 M KCl reduced transport and releases at least two amino acidbinding glycoproteins (19).…”

“…It is probable that both of these treatments disrupt and/or release components necessary for the functioning of active transport. The observations that the general system is the one most sensitive to both enzymatic treatment and glycerol membrane disruption (14) suggest that this permease may be more exposed to the external environment of the cell and/or less firmly attached to the cell surface.…”