Spectrophotometric quantitation of protochlorophyll(ide): Specific absorption and molar extinction coefficients reconsidered

To allay doubt about how to calculate molar extinction eoeffieients from the specific absorption coefficients of protoehlorophyll(ide), dark‐grown leaf segments and saponin protochlorophyll(ide) holochrome subunits frotn barley (Hordeum vulgare L.) and cotyledons of cucumber (Cucumis sativus L.) were extracted with acetone without or following prior, brief illumination. Absorbance data and eoeffieients of chlorophyll a were used to derive extinetion eoeffieients of protoehlorophyll(ide); 626 nm (range: 30 to 35 1 mmol‐1 cm‐1) without recourse to published coefficients c protochlorophyll(ide). These results combined with evaluation of how the origin; coefficients were obtained, argue for using the molecular weight of protochlorophy rather than protochlorophyllide to calculate molar extinction eoeffieients from th specific absorption coefficients.