Oxidation of Glucose, Ribose, Alanine, and Glutamate by Leishmania braziliensis panamensis1

Abstract

The metabolism of [1-14C]- and [6-14C]glucose, [1-14C]ribose, [1-14C]- and [U-14 C]alanine, and [1-14C]- and [5-14C]glutamate by the promastigotes of Leishmania braziliensis panamensis was investigated in cells resuspended in Hanks'' balanced salt solution supplemented with ribose, alanine, or glutamate. The ratio of 14CO2 produced from [1-14C]glucose to that form [6-14C]glucose ranged from about two to six, indicating appreciable carbon flow through the pentose phosphate pathways was further demonstrated by the production of 14CO2 from [-14C]ribose although the rate of ribose oxidation was much lower than the rate of glucose oxidation. The rate of 14CO2 production from [1-14C]glucose was almost linear with time of incubation, whereas that of [6-14C]glucose accelerated, consistent with an increasing rate of flux through the Embden-Meverhof pathway during incubator. Increasing the assay temperature from 26.degree.C to 34.degree.C had no appreciable effect on the rates or time courses of oxidation of either [1-14C]- or [6-14C]glucose or of [1-14C]ribose. Both alanine and glutamate were oxidized by L. b. panamensis, and at rates comparable to or appreciably greater than the rate of oxidation of glucose. The ratios of 14C2 produced from [1-14C]- to [U-14C]alanine and from [1-14C]-to [5-14C]glutamate indicated that these compounds were metabolized via a functioning tricarboxylic acid cycle and that most of the label that entered the tricarboxylic acid cycle was oxidized to carbon dioxide. Heating the cultures for 6 or 12 h at 34.degree.C, which converts the promastigotes into an ellipsoidally shaped intermediate form, decreased the rates of oxidation of glucose, alanine, and glutamate. The oxidation of glutamate decreased by about 50% and 70% after a 6-h or 12-h heat treatment, respectively. Returning the heated cultures to 26.degree.C initiated a reversion to the promastigote form and recovery of the rate of glucose oxidation, but glutamate oxidation did not return to control levels by 19 h at 26.degree.C.