Molecular orientation in quantasomes II. Absorption spectra, hill activity and fluorescence yields

Abstract

The absorption spectrum of spinach quantasomes is compared with those of whole chloroplasts and intact leaves. Using the scattered-transmission technique, it is shown that the absorption maximum at 678.5 mμ in spinach leaves is not shifted in the preparation of isolated chloroplasts or by sonication and separation of small quantasome aggregates.

The effects of several organic compounds and surface-active agents on the absorption spectra, chlorophyll fluorescence and Hill-reaction activity of quantasomes fall into two general classes. Added acetone, methanol, urea or sodium dodecyl sulfate induce a loss in Hill activity at appreciably lower concentrations than are required to give a pronounced fluorescence increase or blue shift in the absorption maximum at 678 mμ. On the other hand, quantasomes treated with Triton X-100 retain Hill activity at higher concentrations of the non-ionic detergent than are necessary to produce pronounced absorption and fluorescence changes. The principal conclusions reached are: (1) the position of the chlorophyll maximum in the red is not a sensitive measure of the ability of photosynthetic materials to carry out the Hill reaction, (2) energy diverted from normal photochemical pathways does not in general immediately appear as enhanced fluorescence, and (3) detergent concentrations comparable to the chlorophyll concentrations of quantasome aggregates are capable of profound effects on physical properties.