Ethanol is one of the products of the metabolism of glucose by Candida albicans. The amount produced is directly related to the concentration of glucose in the medium. The fungus utilizes ethanol as a sole source of carbon but is relatively intolerant of ethanol in its environment. Ethanol induces germ tube formation by blastoconidia of C. albicans. Germination was not seen under fermentation conditions even though the amount of ethanol produced was in the range form stress proteins that are similar to heat shock proteins. The possibility that stress proteins may regulate germ tube formation by C. albicans is discussed.

Blastospores of Candida albicans germinated in a proline-biotin-buffer medium incubated at 37 C. Certain other amino acids in the glutamate, aspartate, and pyruvate families also fostered germination but generally to a lesser extent than did proline. L-Cysteine, D-proline, and certain structural analogues of Lproline inhibited proline-stimulated germination. The concentration of phosphate and glucose was crucial to amino acid-stimulated germination of C. albicans. Clinical isolates and stock cultures varied in their response to the germ tube-inducing activity of proline or other amino acids. The proline-buffer medium cannot be used in a diagnostic test for production of germ tubes by isolates of yeasts.

391~ L-Proline entered both mycelial and yeast cells of Candida albicans by an active transport system of high specificity at low ((0.1 mM) external concentrations of substrate. The apparent K, value of this system was 0-1 mM for both types of cells, while the Vvalue was 4 nmol min-' (mg dry wt)-' for mycelial cells and 1-4 nmol min-l (mg dry wt)-' for yeast cells. At L-proline concentrations greater than 0-1 mM, the amino acid appeared to enter both morphological forms by diffusion as well as active transport. As saturation was approached diffusion became increasingly important. The higher uptake rate of mycelial cells seemed not to be the result of an inducible system. The optimal pH and temperature for transport of L-proline were 7-0 and 37 O C , respectively. Sodium azide and the proline analogues sarcosine and L-azetidine-Zcarboxylic acid inhibited L-proline uptake, while ~-thiazolidine-4-carboxylic acid was less effective. The active transport system was highly specific for L-proline since neither ammonium ions, which inhibit the general amino acid transport system of fungi, nor 16 different amino acids interfered substantially with uptake.

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