Basic amino acids and inorganic polyphosphates in Neurospora crassa: independent regulation of vacuolar pools

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Abstract
At least 78% and perhaps all of inorganic polyphosphate is contained within the vesicles (vacuoles) of N. crassa, where over 97% of the soluble arginine, lysine and ornithine pools accumulate. Synthetic polyphosphate can concentrate arginine up to 400-fold from dilute (0.01 mM) solutions in equilibrium dialysis. For these reasons and because the molar ratio of basic amino acids and polyphosphate P is approximately 1, the hypothesis that there was an obligate physiological relationship between them was tested. Experiments in which N starvation and arginine excess were imposed upon cells showed that polyphosphate content was insensitive to changes in the basic amino acid content. Experiments involving phosphate starvation and restoration showed that basic amino acid content was almost wholly independent of polyphosphate pools. The normal high degree of compartmentation of arginine in vesicles was maintained despite polyphosphate depletion, and arginine was still exchanged across the vesicular membrane. N. crassa, like yeasts, can regulate polyphosphates and basic amino acids independently. The accumulation of basic amino acids in vesicles may depend on an energy-requiring mechanism in addition to the demonstrated charge interaction with polyphosphate.