Pyrroles and related compounds. Part XXXII. Biosynthesis of protoporphyrin-IX from coproporphyrinogen-III

Abstract

New syntheses of 4,6,7-tris-(2-methoxycarbonylethyl)-1,3,5,8-tetramethyl-2-vinylporphyrin (2c) and its 4-vinyl isomer (2d), from pyrromethanes, are reported. These porphyrins and coproporphyrin-III tetramethyl ester (2b) were labelled at the meso-positions with tritium, and incubated in the form of the porphyrinogen carboxylic acids, with a cell-free system from Euglena gracilis. Coproporphyrinogen-III (3b), the standard for the system, was incorporated into protoporphyrin-IX (1a) to the extent of 2·0%, whereas the 2- and 4-vinylporphyrinogens gave incorporations of 3·0 and 0·5%, respectively. These results show conclusively that, in the biosynthesis of protoporphyrin-IX from corproporphyrinogen-III in Euglena gracilis, the 2-propionic acid group is converted into vinyl before the 4-substituent is modified. Further confirmation was obtained by detection of radiochemically labelled 2-vinylporphyrinogen (3c)[by isolation of the corresponding porphyrin (1c) using dilution analysis] as a product of the coproporphyrinogen-III feeding; the isomeric identity of the porphyrin (1c) was established using high-pressure liquid chromatography.