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

The metabolism of 1-¹⁴C]- and 6-¹⁴C]glucose, 1-¹⁴]ribose, 1-¹⁴C]- and U-¹⁴C]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 from 6-¹⁴C]glucose ranged from about two to six, indicating appreciable carbon flow through the pentose phosphate pathway. A functional pentose phosphate pathway was further demonstrated by the production of ¹⁴CO₂ from 1-¹⁴C]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-Meyerhof pathway during incubation. Increasing the assay temperature from 26°C to 34°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 ¹⁴CO₂ 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°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°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°C.