Lipophilic interaction between thylakoid membranes and aliphatic compounds

Spinach chloroplasts pre-incubated at various temperatures, changed their photosynthetic activities (measured at 15°C) as the incubation temperature was raised; these activities showed characteristic activitytemperature profiles as follows:

1. The profiles were shifted to lower temperatures if various aliphatic compounds were present in the incubation mixture.
2. In general, the extent of the shift was proportional to the product of the concentration and the partition coefficient of the compound, i.e. to the concentration of the compound partitioned in the lipophilic chloroplast phase.

The combined effects of heat and the aliphatic compounds tested indicated that the lipophilic groups in these compounds play a determinative role in the heat denaturation of thylakoids. The consequence of such structure alterations is inactivation of photosynthetic functions. The lipophilic properties of the spinach thylakoid membrane as compared with certain artificial and natural membranes are described.