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pubmed:abstractText |
In submerged grown hyphae of Penicillium cyclopium the activities of seven transport systems could be distinguished which share in the uptake of L-arginine, L-glutamic acid, L-phenylalanine and L-leucine. They include the specific systems a (accepting L-arginine and L-lysine), b (L-phenylalanine, L-tyrosine), c (L-glutamic acid) and d (L-leucine), system I (a 'general amino-acid permease') and the low-affinity systems II and III, which accept acidic or basic amino acids, respectively, but also L-phenylalanine. In nutrient-sufficient cells, systems I, II and III remain repressed; uptake is dominated by the specific systems b, c, d and a, the latter reaching its maximum activity. Nitrogen starvation is the most powerful signal for the development of systems I, II and III, whereas, in carbon-starved cells, systems b, c and d reach maximum activities. The development of the general amino-acid permease in nitrogen-starved cells requires both translational and--with a few hours delay--transcriptional events as indicated by the influence of cycloheximide and 5-fluorouracil. The uptake of all amino acids is accompanied by a transient acidification of the cellular interior. Short-time preaccumulation of several anions, such as citrate, alpha-oxo-glutarate, glutamate (but not glutamine), increases the initial rate of amino-acid uptake at a pH above the optimum. Uncouplers inhibit the uptake not only under aerobic but also under anaerobic conditions, where the ATP content is not influenced by these compounds. These findings point to an H+/amino acid symport, which is tightly connected with the recycling of the incoming protons by the plasmalemma H+-ATPase.
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