Transport of B-Vitamins in Microorganisms. VII. The Uptake of 14C-Niacinamide by Non-proliferating Cells and by Protoplasts of Streptococcus faecalis.

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Abstract
Non-proliferating cells of S. faecalis were incubated with labelled niacinamide under varying conditions and the radioactivity retained by the carefully washed cells was measured. Selected uptake studies were, in a similar way, carried out with protoplasts prepared by lysozyme treatment. Extracts from the labelled cells and protoplasts were subjected to paper chromatog-raphy. Although most of the labelled niacinamide was rapidly after the uptake converted to other compounds, estimations of the intra-cellular and extracellular concentrations indicated that the accumulation of niacinamide proceeds against considerable concentration gradients. The uptake of niacinamide in both, non-proliferating cells and in protoplasts, exhibited also several other characteristics of active transport, viz-dependence on pH and on a supply of metabolic energy, as well as saturation kinetics. The accumulation capacity of the non-proliferating cells with respect to labelled niacinamide varied inversely with the niacinamide content of the growth medium. The uptake in protoplasts was considerably affected by K+, Mg3+, and Ca2+, whereas the uptake in intact cells was much less sensitive to these agents.