Mg-protoporphyrin-IX and delta-aminolevulinic acid synthesis from glutamate in isolated greening chloroplasts. Mg-protoporphyrin-IX synthesis

A crude plastid preparation from greening cucumber cotyledons was able to accumulate Mg-protoporphyrin-IX when incubated in the presence of glutamate. ¹⁴C from l-U-¹⁴C]glutamate was incorporated into the porphyrin. The product was identified by its emission and excitation fluorescence spectra and by its chromatographic behavior on cellulose thin layers. The biosynthesis had a marked requirement for ATP and O₂. α,α′-Dipyridyl, a metal ion-chelating agent which had been shown to stimulate the synthesis of Mg porphyrins and phorbins in etiolated bean leaves and other whole tissues, stimulated likewise the in vitro synthesis of Mg-protoporphyrin-IX by isolated greening chloroplasts. Freezing and thawing, which destroy organelle integrity, abolished the ability of these isolated plastids to biosynthesize Mg-protoporphyrin-IX.