In vitro binding of 2-acetaminofluorene to RNA and protein with rat liver microsomes

Covalent binding of 2-acetaminofluorene[9-14C] with exogenous Torula yeast RNA and endogenous protein was investigated in liver microsome system in vitro. The binding to protein was 100 times higher than that to RNA. Requirement of NADPH, effectiveness of methylcholanthrene treatment, and inhibition by 7,8-benzoflavone suggest possible involvement of mixed-function oxidases in this binding. The binding was not due to contaminated cytosol in the microsome fraction. Addition of cytosol, sulfate ion, and ATP diminished the binding. Parallel experiments using N-hydroxy-2-acetaminofluorene[9-14C] denied major contribution of this metabolite to the binding of 2-acetaminofluorene in the microsome system. Ring-hydroxylated product was suggested as a possible metabolite for the binding.

Interactions between Bifidobacterium bifidum N4 and Escherichia coli K-12 in their mixed cultures

The interactions between Bifidobacterium bifidum N4 (B. bifidum) and Escherichia coli K-12 (E. coli) were investigated in their mixed cultures. Under conditions in which both bacteria grew well in their pure culture, B. bifidum inhibited the growth of E. coli even when the latter was inoculated at 10(4)-fold and preincubated for 41 hr. The inhibition in the mixed cultures appeared when the pH values were reduced below 4.6. When the lowering of pH was prevented by the addition of NaOH, no inhibition was observed. At the same initial pH of 6.5, lactic acid and acetic acid, metabolites of B. bifidum, had more inhibitory effect on the growth of E. coli than other aliphatic fatty acids. On the other hand, in the mixed cultures with E. coli, B. bifidum grew in the absence of its essential vitamins, riboflavin and pantetheine and, furthermore, aerobically.