Protochlorophyll Biosynthesis in a Cell-free System from Higher Plants

Abstract

A cell free system prepared from etiolated cucumber (Cucumis sativus, L) in tris-sucrose buffer is able to incorporate δ-aminolevulinic acid-4- ¹⁴C into the two components of protochlorophyll: protochlorophyllide and protochlorophyllide ester. The activity is associated with the etioplasts. Optimal incorporation is obtained at pH 7.7. For the formation of protochlorphyllide ester, oxygen, reduced glutathione, methyl alcohol, magnesium, inorganic phosphate, and nicotinamide adenine dinucleotide are required. For the formation of ¹⁴C-protochlorophyllide, adenosine triphosphate, and coenzyme A are required in addition to the above. The requirement for methyl alcohol is highly specific, and the methyl group appears to be incorporated into the protochlorophyll molecules. A biosynthetic scheme resulting in the parallel production of ¹⁴C-protochlorophyllide and ¹⁴C-protochlorophyllide ester from ¹⁴C-Mg protoporphyrin monoester is presented.