Photorubin, the light-dependent water-soluble pigment formed by Saccharomyces cerevisiae var. ell@soidsus, is in close relationship with ~ diazotable amine absorbing at 540 mg after the Bratton-Marshall reaction.
The culture liquids of the photorubin-negative strains (deficient in histidine synthesis) obtained by hybridization do not contain diazot~ble amines and have only one peak at 248 m~ in their ultraviolet absorption spectra. Back mutants to photorubin-positivity and the wild type do contMn diazotable amines and or have only one peak at 282 m~.
The addition of p-aminobenzoic acid to the growth medium reduces photorubin formation, whereas histidine exerts the opposite effect.
Photorubin is the orange-red pigment formed by all the wild strains of Saccharomyces cerevisiae var. ellipsoideus; it appears whenever, after the cessation of growth, the colorless liquid media are exposed to light (ZAMBO~V~LLI and ZAsI, 1965). This pigment is probably the same as that observed by En~Bw~G and K~ur (1964) in studies on the influence of light upon the development of yeasts. Photorubin-negative strains, obtained by hybridization, were crossed with wild strains : the character is transmitted according to Mendelian heredity; hybrids Phr β’ 19hr are photorubin-positive (phenotype Phr) and segregate the character with a ratio 2:2 (ZA~I and ZA~BO~SLT.I, 1965). Subsequently it was ascertained that photorubin-negative strains require histidine for growth (ZA~BO~ELLI, 1966).
According to recent studies by AM~s etal. (1960), A~]~s etal. (i961), MARTIN (1963), SMrr~ and A~s (1964, 1965), the biosynthesis of histidine in Salmonella typhimurium starts with ATP and PRPP (5-phosphoribosyl-l-pyrophosphate) to bring about, at first and through passages still partly unknown, the formation of 5-amino-4-imidazolecarboxamide ribonucleotide (AICAR or AIC-R-P) and imidazoleglycerol phosphate (IGP) according to the following pathway: Mg++