Magnesium protoporphyrin

Esterification of the propionic acid side chain at C-13 (ring C) with a methyl group catalyzed by S-adenosyl-L-methionine-magnesium protoporphyrin 0-meth-yltransferase yields protoporphyrin IX monomethyl ester (MPE), which originates protochlorophyllide by a P-oxidation and cyclization of the methylated propionic side chain. This molecule contains a fifth isocyclic ring (ring E), the cyclopentanone ring that characterizes aU chlorophylls. 

This enzyme [EC 2.1.1.11] catalyzes the reaction of S-adenosylmethionine with magnesium protoporphyrin to produce S-adenosylhomocysteine and magnesium protoporphyrin monomethyl ester. 

SOLUBILITY PRODUCT Magnesium phosphate (Mg3(P04)2>, SOLUBILITY PRODUCT Magnesium protoporphyrin,... 

Magnesium protoporphyrin dimethyl ester. Crude product... 

This reaction does not occur readily spontaneously but is catalyzed by an ATP-dependent magnesium protoporphyrin chelatase.419 422 Subsequently, the carboxyethyl side chain on ring C undergoes meth-ylation (Fig. 24-23, step b) and (3 oxidation (step c). 

The biochemical conversion of magnesium protoporphyrin mono-methylester to protochlorophyll probably also involves the primary formation of a jr-cation radical [Cox (41)]. Whether the hydrogenation of protochlorophyll to chlorophyll involves phlorin intermediates [Woodward (214)] is still not known. 

Fig. 2.16 Chlorophyll biosynthesis from protoporphyrin IX to magnesium protoporphyrin IX-13-methylpropionate.

Magnesium protoporphyrin dimethyl ester [14724-63-1] M 580.7, m 214-217 (others found m 228-230 ). 

Figure 1. A photoaffinity label containing magnesium protoporphyrin IX...

Scheme 14.31. A representation of the incorporations of metals (Fe and Mg ) into protoporphyrin IX to prodnced heme (protoheme) and magnesium protoporphyrin IX, respectively. The latter is the precnrsor for chlorophyll. EC numbers and some graphic materials in this scheme have been taken from links in http //www.chem.qmul.ac.uk/iubmb/enzyme.

Also, as shown in Scheme 14.31, incorporation of magnesium with the aid of magnesium chelatase (EC 6.6.1.1.) leads to magnesium protoporphyrin IX, now committed to the biosynthesis of chlorophyll. 

Biosynthesis.—Further evidence has been adduced for the formation of 5-ALA and magnesium protoporphyrin-IX from glutamate in greening plants,and the enzymic preparation of the monomethyl ester of magnesium protoporphyrin has been described." Intermediates in the last stages of chlorophyll biosynthesis in which the geranylgeranyl side-chain is converted into phytyl have been studied l- C-labelled acetate is incorporated into the expected alternate positions in the phytyl ester side-chain (as shown by C n.m.r. spectral studies), but only low incorporations of mevalonate were obtained, presumably because of poor transport into the cell. The biosynthesis of chlorophyll-f has also been studied." ... 

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