Presence of Compounds containing Iron in the Digestive System

Abstract

PROBLEMS concerned with iron storage and its subsequent utilization by invertebrates have, most often, concentrated on those forms in which haemoglobin is present^1–10 and in certain instances in those organisms in which haemocyanin is utilized as a respiratory pigment¹¹. Reports have shown that when haemoglobin is utilized as a respiratory pigment it is demonstrable not only in the body fluid of the animal but also in a variety of tissues—muscle, nerve and eggs⁶, as well as fat cells¹². In some cases, such as Daphnia magna which is actively losing haemoglobin, porphyrins are not demonstrable, but loosely bound iron is easily demonstrated histologically in the walls of the gut caeca, in the fat cells and in the maxillary glands¹³. In certain organisms possessing the copper blood pigment haemocyanin it has also been possible to demonstrate the presence of iron porphyrin compounds (haemochromogens) not only in the blood but also in such diverse structures as the eggs of Limulus polyphemus, the radula muscle and heart of Busycon canaliculatum (both myoglobin and cytochrome being present), cytochromes in the heart, claw and skeletal muscle of Homarus americanus, and cytochromes in many of the tisssues of Loligo peali¹¹. Conclusions drawn from these many experiments indicate that, except for the substitution of haemocyanin for haemoglobin, oxygen utilization is essentially the same as in mammals. They also point out that these animals are utilizing iron in the synthesis of certain porphyrin compounds of the cytochrome system. It has thus been fairly well established that possession of haemoglobin as a respiratory pigment is no prerequisite for the presence of compounds containing iron in animal tissues.