SPECTROFLUOROMETRIC DETERMINATION OF Mg‐PROTOPORPHYRIN MONOESTER AND LONGER WAVELENGTH METALLOPORPHYRINS IN THE PRESENCE OF Zn‐PROTOPORPHYRIN*

Greening tissues accumulate Mg‐protoporphyrin monoester and a group of metalloporphyrins that exhibit fluorescence emission and excitation properties which are red‐shifted with respect to Mg‐protoporphyrin monoester. These metalloporphyrins are collectively termed longer wavelength metalloporphyrins and are presumed to be metabolic intermediates between Mg‐protoporphyrin monoester (MPE) and protochlorophyllide. The longer wavelength metalloporphyrins, together with Mg‐protoporphyrin monoester, are referred to as the MPE‐equivalent. During the study of the biosynthesis of the components of the MPE‐equivalent and the study of their conversion to protochlorophyllide in vitro, it was observed that Zn‐protoporphyrin and its monoester were also formed. The latter compounds interfered with the determination of the MPE‐equivalent. Simultaneous equations were derived and solved to yield an equation which permitted the determination of the amount of MPE‐equivalent in the presence of Zn‐protoporphyrins from the fluorescence emission spectrum of the mixture. Such determinations were made without prior segregation of the metalloporphyrins.