The Endogenous Metabolism of Euglena gracilis

Abstract

SUMMARY: The endogenous respiratory rate of non-photosynthetic Euglena gracilis var. bacillaris is remarkably constant under varied conditions of growth and incubation. After 60–90 min. of slightly more rapid respiration, the endogenous oxygen uptake averages about 6.5 μl. O2/million cells/ hr., and this rate can be maintained for at least 26 hr. The respiratory quotient of the endogenous metabolism is 1.0. Fluoroacetate inhibits endogenous oxygen consumption about 70%. A variety of evidence suggests that the polysaccharide paramylum is the major endogenous substrate. Tracer experiments indicate that the endogenous metabolism continues during the oxidation of exogenous substrates, but that the assimilated substrate mixes with, and dilutes the endogenous reserves. The time-course of this dilution process indicates that the most recently assimilated reserves are the first to be oxidized.