Magnesium 2,4-Divinylphaeoporphyrin A5 Monomethyl Ester, a Protochlorophyll-Like Pigment Produced by Rhodopseudomonas Spheroides

The identification of intermediates in the biosynthesis of chlorophyll has been largely dependent upon the use of mutants of Chlorella that are unable to synthesize chlorophyll but accumulate in the medium various tetrapyrrole compounds assumed to be precursors (for a review see Granick & Mauzerall, 1961). In particular, Granick (1950) identified magnesium vinylphaeoporphyrin a5 monomethyl ester (Scheme 1, formula V) as an intermediate and it now seems likely that it is this compound and not its phytyl ester (protochlorophyll) that is reduced to the oxidation level of chlorophyll. Esterification with phytol follows, yielding chlorophyll a (formula VII) (cf. The detection in Rhodopetudomonas 8pheroides of an enzyme system which methylates magnesium protoporphyrin (formula II)