Effects of external factors on the amino acid pool of Penicillium griseofulvum

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Abstract
The amino-acid pool of P. griseofulvum changed in size and composition in response to downward drifts in pH which occurred during culture on media containing ammonium sulphate as N source. Intracellular accumulation of endogenous [gamma] -aminobutyric acid occurred only when the pH fell below 5.8. An almost complete efflux of amino acids from the mycelium started when the pH fell below 4.0. Oxygen starvation generally enhanced the accumulation of endogenous [gamma] -aminobutyric acid, to a degree which depended on pH during anoxia and on the age and pH of the culture at the time of the removal of oxygen; concomitant depletions of glutamic acid occurred. Removal of oxygen from young cultures, however, inhibited [gamma]-aminobutyric -acid formation and led to an increase in the concentration of alanine. Leakage of amino acids into the medium and alterations in pool composition were observed after the addition of certain growth-inhibitory reagents. When compared with mycelium grown on an inorganic N supply, mycelia grown on single amino acids as sole N sources contained increased amounts of the supplied amino acids; transport against apparent concentration gradients was indicated. Changes in amounts of other pool constituents were induced by some amino acids. Amino acids derived from the medium were more readily washed out of mycelium by water (but not by iso-osmotic medium) than were endogenous amino acids.