THE KINETICS OF FATTY-ACID UPTAKE BY PARAMECIUM-TETRAURELIA

The kinetics of radiolabeled fatty acid uptake by the ciliate Parameci um tetraurelia was examined on a homologous series of saturated, strai ght chain fatty acids of even carbon numbers. Uptake rates increased w ith chain length from acetate to palmitate. Saturation kinetics was de monstrated for most fatty acids examined, thus ruling out simple diffu sion as the major mechanism for fatty acid transport and implicating c arrier-mediated, facilitated transport as the major mechanism. Data fr om most competitive inhibition experiments were too scattered to deter mine the number of transporter systems present. Cholesterol uptake als o exhibited saturation kinetics and hence other sterols, which can sat isfy this nutritional requirement, may also be transported by a carrie r-mediated mechanism. The uptake of the essential fatty acid oleate wa s faster than those observed for the saturated acids and could not be explained by only one transport mechanism. Therefore, fatty acid trans port also occurs via other kinetically significant routes.