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The germination of blastospores of Candida albicans is accompanied by a rise in the intracellular concentration of adenosine 3':5'-cyclic monophosphate (cyclic AMP). Germination was induced either by peptides isolated from seminal plasma or by an amino acid mixture, and both germination and the rise in cyclic AMP required a temperature of 37 degrees C. The rise occurred during the first hour of incubation, but full germination required a temperature of 37 degrees C for 4 h. Germination and the rise in cyclic AMP, in the presence of suboptimal concentrations of inducers, were stimulated by theophylline. Pre-incubation of cells with dithiothreitol in the absence of inducers inhibited subsequent germination but not the rise in cyclic AMP. Germination and the rise in cyclic AMP were inhibited if dithiothreitol or N-succinimidyl-3-(4-hydroxyphenyl)propionate was present during the induction period.

A glycopeptide and a peptide have been isolated from bovine seminal plasma which together will induce germination of Candida albicans blastospores at 37 degrees C and in the presence of glucose and Mn2+. ¿They have molecular weights of 2000 to 3000. Both peptides contain appreciable amounts of aspartic and glutamic acids, only the glycopeptide contains threonine, lysine, histidine and arginine, while only the peptide contains proline. Acid hydrolysates are fully active in inducing germination and a mixture of aspartic acid, lysine, histidine, threonine, proline and beta-alanine can replace them. Mn2+ is not then required. Amino acid mixtures are required to be present throughout the whole period in the incubation medium for full germination to take place, but the peptides can be removed after 1 h incubation and if the cells are resuspended in a buffered glucose medium full germination occurs after a further 3 h incubation.

Previous work led to the separation from seminal plasma of a peptide fraction which promoted a high rate of germination of blastospores of Candida albicans. It has now been shown that an acid hydrolysate of this material is also highly active. A minimal amino-acid mixture consisting of aspartic acid, lysine, histidine, threonine, proline and beta-alanine gave 90% germination in 4 h with 17 out of 28 strains examined. Glucose and inorganic phosphate were also required. Phosphate was not required for the activity of the original peptide fraction.

The release of acid phosphatase and polysaccharide-peptide complexes by hydrolytic enzymes from the surface of the blastospore and mycelial forms of Candida albicans has been examined in cells from 4 h and 18 h cultures and the results correlated with the appearance of the treated cells in the electron microscope. Treatment with dithiothreitol was necessary for the degradative action of the enzymes to occur. Material released by all the treatments used had a similar qualitative composition, but the proportions of mannan, glucan, peptide and acid phosphatase varied with different treatments and with the type of cell examined. I,3-beta-Glucanase was required for major changes in the cell wall to be effected, but a significant amount of material was released with a chitinase preparation containing some protease activity. Protoplasts were obtained from all types of cell using Cytophaga lytic enzyme L1 which had I,3-beta-glucanase and protease activity, but the purified I,3-beta-glucanase and protease prepared from Streptomyces violaceus cultures required the presence of a chitinase before protoplasts were released. The bonding association between the major components which comprise the cell wall, and the spatial distribution of these macromolecules, varies appreciably between the two dimorphic forms and with the age of the culture.