Concerning the Naturally Occurring Porphyrins

Evidence for a dualism of the porphyrins in nature has been repeatedly presented by Hans Fischer (1, 2, 3). This means that both plant and animal organisms are capable of the formation of porphyrins of two isomeric series, those corresponding to aetioporphyrin III, including hemoglobin and chlorophyll, and those of the aetioporphyrin I type, the function of whose representatives is as yet very little understood. The aetioporphyrins, of which there are four, have only methyl and ethyl groups in varying position on the porphyrin ring. Because of this relative simplicity Fischer has classified the isomers of the other porphyrins according to which aetioporphyrin their structure corresponds. The aetioporphyrins are artificial. Porphyrins corresponding in structure to aetioporphyrins I and III have been found in nature, those corresponding to II and IV have only been obtained artificially. Fischer has pointed out that it is chemically inconceivable for porphyrins of the one type to be transformed into those of the other except by complete destruction and re-synthesis. Thus it is necessary to look upon the formation of the two series occurring in nature as independent processes. Porphyrins corresponding to aetioporphyrin I were first isolated from the urine and feces of a case of congenital porphyrinuria by H. Fischer (4). These were named coproporphyrin I and uroporphyrin I, the former having four methyl and four propionic acid groups, the latter eight carboxyl groups. Several instances of the same disease have since been studied by Fischer and Duesberg (5), and also Van den Bergh (6), in which identical porphyrins were excreted. However, one instance was reported by each in which coproporphyrin III was isolated. Thus evidence for the existence of two chemically different, but