Fig 5.

G3P and DHAP substrate specificity profiles in purified R. prowazekii. Initial linear rates of transport of [¹⁴C]G3P (20 μM) and [³²P]DHAP (10 μM) in the absence or presence of candidate substrates were determined with purified R. prowazekii suspended in modified SPGMg²⁺ buffer at 34°C. Data points are presented for each time point as a percentage of the rate of either G3P or DHAP transport in the absence of any other candidate substrate. The data shown are averages of technical triplicates of at least three independent rickettsial preparations. The substrate specificity of the G3P and DHAP transport systems was assayed by testing putative candidate substrates to determine if they behave as competitive inhibitors of either G3P or DHAP transport. Each putative candidate substrate was added at a concentration of 20 times the reported K_t of each for G3P (K_t, ∼40 μM) and DHAP (K_t, ∼6 μM). For each candidate substrate that displayed inhibition of either G3P or DHAP transport, a K_i was estimated by an algebraic manipulation of the modified Michaelis-Menten equation for determining velocity in the presence of an inhibitor {v_i = (V_max[S])/([S] + K_m(1 + ([I]/K_i)⁻¹, where [S] is the substrate concentration and [I] is the inhibitor concentration} and reported in the table below the corresponding data in italic font for G3P and bold font for DHAP. Error bars represent the standard deviations of the means. Abbreviations: ND, not determined; G2P, glycerol-2-phosphate; 3PGA, 3-phosphoglycerate; Ga3P, glyceraldehyde-3-phosphate; Pi, inorganic phosphate; GLYC, glycerol; DHA, dihydroxyacetone; R5P, ribose-5-phosphate; G6P, glucose-6-phsophate; FOS, fosfomycin.