Methionine flux between a tapeworm (Hymenolepis diminuta) and its environment

Abstract

In the course of work designed to measure the extent to which methionine absorbed in one region of a tapeworm became distributed throughout the strobila, it was observed that, whereas, in saline, Hymenolepis diminuta lost previously absorbed methionine slowly, in the intestine of a rat the methionine was lost very rapidly. The fact that two worms containing initially the same amount of free methionine should, after a short period in different environments, contain utterly different quantities of methionine indicated that the quantity of a free amino acid present at any time is not simply dependent on the amount previously absorbed less the amount metabolized.This observation has a bearing on several aspects of tapeworm physiology. Do tapeworms normally absorb amino acids from the intestine during periods of high concentration and release them when the concentration falls? If they do, the presence of tapeworms in the intestine could be beneficial to the host by extending the period over which an amino acid is available to the host, an important point as a mammal is unable to store amino acids for more than a few hours (Gitler, 1964). A knowledge of the environmental conditions which influence the level of free amino acids in a tapeworm, and thereby its ability to synthesize proteins, is obviously also of critical importance to workers attempting to grow worms in vitro.