Transport of pantothenic acid in Lactobacillus plantarum

Abstract

The characteristics of pantothenic acid (PA) transport into nonproliferating cells of Lactobacillus plantarum were studied. These characteristics included the effects of pH and temperature variations and the energy requirement for transport and binding of the vitamin. At pH 7.5 and 38 °C the intracellular vitamin was in the form of phosphopantothenic acid (P-PA) and was not exchangeable with external PA. Vitamin transport appeared separate from phosphorylation since significant free PA was observed only at elevated temperatures (e.g. 45 °C) and at low pH values. PA uptake and accumulation were energy-dependent, being inhibited completely by 10−2 M iodoacetate and the absence of glucose, exhibited pH and temperature optima of 7.5 and 38 °C, respectively, and were linear with time for at least 60 min. PA uptake exhibited substrate saturation. No free PA was observed when cells were incubated in PA concentrations above saturation levels. Apparent Km and Vmax values of 7.85 × 10−7 M and 5.35 μmol of PA/mg cells (dry weight) per minute, respectively, were determined from Lineweaver–Burk plots. Competitive inhibition of transport was observed with panthenol and pantoyl taurine. Ki values were, respectively, 3.55 × 10−5 M and 3.07 × 10−6 M. Pantoyl lactone, at concentrations which inhibited growth by 78%, had no effect on transport. The data reported suggest that PA transport is an active, mediated process and that transport may limit the phosphorylation of PA into P-PA. Inhibitor studies showed that PA transport was at least 150 times more sensitive to analogue inhibition than was growth itself, suggesting that transport of PA was not a limiting factor in the growth of L. plantarum.