Studies in carotenogenesis. 6. The effect of some possible carotene precursors on growth, lipogenesis and carotenogenesis in the fungus Phycomyces blakesleeanus

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Abstract
When mats of Phycomyces are transferred to media containing various concns. of glucose, carotene synthesis does not begin until the concn. is between 0.75 and 1.0% (wt./vol.). A large no. of substances tested for ability to stimulate carotenogenesis in transferred cultures all gave negative results. In growing cultures containing 1.0% (wt./vol.) glucose, carotenogenesis was stimulated slightly by alpha -ketoisocaproic and alpha-hydroxyisocaproic acids and appreciably by beta-methylcrotonaldehyde (all at concns. of about 0.001%); isovaleraldehyde and beta-methylcrotonic acid were without obvious effect, when tested at the same level. Tested at higher levels a no. of binary mixtures, thought likely to give rise to beta-methylcrotonaldehyde, were inactive. The following were extremely toxic to Phycomyces at a concn. of about 0.02% (wt./ vol.): isolvaleric, isocaproic, alpha-ketoisocaproic and alpha-methylcrotonic acids, and beta-methylcrotonaldehyde and crotonaldehyde. Both alpha-hydroxylation and amidation of isocaproic and isovaleric acids rendered them non-toxic. Isovaleraldehyde was much less toxic than beta-methylcrotonaldehyde, while isoamyl alcohol was non-toxic.