The action spectrum from 232 to 687 nm was determined for the transformation of protochlorophyllide into chlorophyllide a in solutions of protochlorophyll holochrome Fran bean leaves. The whole ultraviolet region is effective. The peaks at 445 and 639 nm have a height ratio of 4.0. Only radiation absorbed in the protochlorophyllide itself is effective in transformation (absorption in aromatic amino acids of the protein and in carotenoids is ineffective). The activation spectra for fluorescence at 643 and 683 nm are measured for the holochrome before and after transformation, as well as the change in absorption spectrum that takes place upon transformation. By combining the various measurements the spectrum of inactive (non‐transformable) protochlorophyllide (peak at 440 nm) and the holochromatic chlorophyllide a are derived. In the latter spectrum the peaks at 419 and 435 nm are of about the same height. Copyright © 1969, Wiley Blackwell. All rights reserved
