Intermediates in the Formation of the Chlorophyll Isocyclic Ring

Publisher Website
Google Scholar
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-.beta.-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-.beta.-ketopropionate analog as the substrate. X was identified as the 6-methyl-.beta.-hydroxypropionate analog of Mg-Proto Me by conversion to the dimethyl ester with CH2N2 and comparison with authentic 6-.beta.-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-.beta.-hydroxy and the 6-.beta.-ketopropionate esters in agreement with earlier suggestions.