PHYSIOLOGY OF THE VINEGAR EEL, TURBATRIX ACETI (NEMATODA). I. OBSERVATIONS ON RESPIRATORY METABOLISM

¹ Department of Zoology, University of Oklahoma, Norman, Oklahoma
² Department of Biology, Rice University, Houston, Texas

1. Suspensions of intact Turbatrix aceti in phthalate or phosphate buffer consume oxygen at a rate varying from about 50 to 200 µ1./mg. (tissue nitrogen)/hr. The rate depends on the time lapse between removal of the organisms from the original culture and the beginning of the measurement, i.e., the time without exogenous substrate.

2. Oxygen consumption of intact organisms is markedly stimulated by acetate and also by oxalacetate.

3. Citrate, succinate and malate do not stimulate the oxygen consumption of intact T. aceti at pHs 3.0, 4.5 or 6.0 and when tested with organisms showing several levels of endogenous respiration.

4. Malonate at a concentration of 0.001 M or 0.02 M does not inhibit the endogenous oxygen consumption of intact T. aceti nor does it prevent the stimulation of respiration by acetate.

5. Citrate is synthesized by intact organisms in the presence of acetate. Fluoracetate increases this synthesis and inhibits the respiration of intact vinegar eels.

6. Pyruvate, -ketoglutarate, succinate, malate and oxalacetate are not oxidized by homogenates of T. aceti fortified with cofactors necessary for oxidation of these compounds by mammalian liver preparations.

7. When phenazine methosulfate is used to transfer electrons from pyridine-nucleotides to dichloroindophenol, an active DPN-malic dehydrogenase can be demonstrated in homogenates. TPN has little or no activity. When fumarate is used in place of malate in this system, activity is low, indicating a low fumarase activity.

8. Using phenazine methosulfate to accept electrons from the enzyme, with dichloroindophenol as terminal electron acceptor, a low succinic dehydrogenase activity can be shown in T. aceti homogenates.

9. Isocitric dehydrogenase was not detected in a system containing phenazine methosulfate and dichloroindophenol as electron acceptors and either TPN and Mn⁺⁺ ions or DPN and AMP as cofactors.

10. These findings suggest that, in addition to the active malic dehydrogenase, T. aceti possesses citrate synthetase and aconitase but apparently has limited ability to carry out other reactions of the tricarboxylic acid cycle. The electron transport system, unlike that of many invertebrates, cannot utilize mammalian cytochrome c.

11. If these interpretations are borne out, T. aceti will be the first animal with a predominantly aerobic metabolism in which the tricarboxylic acid cycle in its usual form has been shown to be absent.