Metabolism of Haemoglobin and Haematin Compounds in Ascaris lumbricoides

M. H. Smith, D. L. Lee

Abstract

Variations in the colour of individual Ascaris lumbricoides from the pig are shown to depend on changes in the concentration of the perienteric fluid haemoglobin. Whilst the concentration of the haemoglobin remains constant for several days when the worms are kept in a saline solution, it is rapidly increased when suitable substrates are added to the medium. These must always include a porphyrin or metalloporphyrin containing a vinyl group. Horse haemoglobin was found to be the most suitable substrate under the experimental conditions. Simpler substances cannot be utilized for haemoglobin synthesis. This is only the second example of inability to synthesize protohaematin which is known in the Metazoa. The distribution of haematin has been studied in whole worms and in histological sections by means of peroxidatic reactions. Only the cuticle and the excretory canal appear to be haematin-free. The amount of haemoglobin in the body wall does not seem to fluctuate like that in the perienteric fluid. More is present in the hypodermal layers and the nerve ring than in the actual musculature. Haematin compounds occur in relatively large amounts in the reproductive system, and have been studied spectroscopically in suspensions of uterine eggs. Consideration of the known reactions of the perienteric fluid haemoglobin with oxygen lead to the conclusion that it cannot be effective as a storer or carrier of oxygen in the metabolism of the worm itself. It is suggested that it represents a metabolic pool of haematin from which other haemoproteins are elaborated, and that the variation in concentration is the result of a mechanism for allowing the worm to store haematin at times when it is present in excess in the gut of the host. It is further suggested that the primary function of this mechanism is to enable a maximal rate of egg laying to be maintained. The haematin content of the eggs and the numbers laid would readily account for the quantity of haemoglobin involved. Although the data are insufficient to enable any generalization to be made at present, there are indications that similar phenomena occur in other ascarids and more distantly related nematodes.