Abstract
Cell-free, organelle-free synthesis of Mg-2,4-divinylpheoporphyrin a5 (MgDVP) from Mg-protoporphyrin IX monomethyl ester (Mg-Proto Me) has been described (Wong and Castelfranco 1984 Plant Physiol 75: 658-661). This system consists of plastid membrane and stromal fractions and requires O2, NAD(P)H and S-adenosylmethionine (SAM). The synthetic 6-methyl-β-ketopropionate analog of Mg-Proto Me was converted to MgDVP by the same catalytic system in the presence of O2 and NADPH. SAM was not required. A compound (X) displaying the kinetic behavior of an intermediate was isolated from reaction mixtures with Mg-Proto Me as the substrate, but not with the 6-methyl-β-ketopropionate analog as the substrate. X was identified as the 6-methyl-β-hydroxypropionate analog of Mg-Proto Me by conversion to the dimethyl ester with CH2N2 and comparison with authentic 6-β-hydroxydimethyl ester. X was converted to MgDVP by the same catalytic system in the presence of O2 and NADPH. We conclude that the conversion of Mg-Proto Me to MgDVP proceeds through the 6-β-hydroxy and the 6-β-ketopropionate esters in agreement with earlier suggestions.
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