Pre-uroporphyrinogen: a substrate for uroporphyrinogen III cosynthetase

Pre-uroporphyrinogen, produced from porphobilinogen by the action of porphobilinogen deaminase has been shown to act as a substrate for the enzyme uroporphyrinogen III cosynthetase, being converted in high yield into uroporphyrinogen III; in the absence of cosynthetase, pre-uroporphyrinogen rearranges chemically to afford exclusively uroporphyrinogen I, and evidence is also presented which demonstrates that the deaminase and cosynthetase function independently and sequentially in the overall conversion of porphobilinogen into uroporphyrinogen III.