THE ROLE OF PURINE BASES AS HISTIDINE PRECURSORS IN Lactobacillus Casei

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Abstract
In agreement with conclusions drawn from sparing effects in nutritional studies, guanine serves as a histidine precursor in L. casei. In this role, C 2 of guanine is transferred into the amidine C (position 2) of the imidazole ring of histidine and is a more direct precursor of histidine than is formate. A significant but much smaller incorporation of C 8 of guanine into histidine also occurs. Incorporation of formate into histidine occurs efficiently only in cells grown with folic acid. In contrast, incorporation of C 2 of guanine occurs equally in cells grown with or without folic acid and consequently appears not to occur via free formate as an intermediate.