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.