Modification of amino acid and sugar transport in uncoupler-adapted Euglena gracilis.

Uncoupler-adapted Euglena gracilis have a greatly impaired capacity to take up and incorporate some exogenously supplied amino acids and sugars. The degree of inhibition varies widely from >90% in the case of valine or glucose to none in the case of histidine. The inhibition is due to a decreased activity of the transport mechanism itself and is not due to either a lesion in the control mechanism for endogenous amino acid or sugar synthesis nor to a direct inhibition of the transport mechanism by uncouplers. No preferential labeling of mitochondrial membranes by [14C]amino acids occurs during the process of adaptation, a time when no cell division occurs. Apparently, during the long time required for adaptation, there occurs no major modification of mitochondrial proteins which could explain the subsequent resistance to uncouplers.