“…The C4-intermediate which condenses with glycine (or a derivative) has not been identified. Succinyl coenzyme A is formed by the a-oxoglutarate oxidase of animal tissues (Sanadi & Littlefield, 1953), and is probably also a product of similar reactions in E8cherichia coli and Azotobacter vinelandii (Gunsalus, 1953;Lindstrom, 1953). So far, however, there is no evidence that succinyl coenzyme A participates in porphyrin synthesis.…”