HEMOGLOBIN, THE HEME PIGMENTS, AND CELLULAR RESPIRATION

Hemoglobin has long been studied as a carrier of oxygen in the blood of vertebrates. More recently (1885) a pigment related to hemoglobin was observed by MacMunn in the cells of a great variety of lower animals which have no hemoglobin either in their cells or body fluids. After long neglect, MacMunn’s observations were recalled, and were confirmed and extended. In addition still another pigment was dis-covered which is related to hemoglobin and which in cells acts as a re-spiratory catalyst. A group of pigments called heme pigments and closely related to hemoglobin is accordingly now known. They exist in all aerobic cells where one of them, at least, plays an essential r81e in cellular oxidations. This review is concerned with the chemical proper-ties and biological behavior of heme pigments. Hemoglobin will be included in the discussion because knowledge of the pigments is largely based on a wide study of hemoglobin and its derivatives. Hemoglobin itself is a compound of a colorless protein, globin, and an iron porphyrin pigment. In general the pigments formed by the combination of iron with the various porphyrins are called hemes. The functions of the heme pigments have attracted investigators with very varied interests so that they have been studied from many differ-ent points of view. In organic chemistry their constitution has been of interest; in physiology their chemical properties were analyzed first in order to understand the respiratory functions of the blood, and more recently in connection with the problems of cellular respiration; in physics, at least in the case of one investigator, they have been studied because of their clearly defined spectroscopic properties; in pharma-cology because of their reactions with drugs and poisons; and in natural history because of their wide distribution in nature. These investigations of the heme substances may be considered to have been along four lines