Rates of tissue uptake of palmitic acid-1-14C complexed with albumin by two different procedures.

The effect was investigated of two different methods of preparing an albumin-palmitic acid complex on the tissue uptake of the palmitic acid, both in vivo and in vitro. Complex A was prepared by exposing monomolecular layers of palmitic acid-1-(14)C deposited on a solid surface to albumin dissolved in buffer. Complex B was prepared by the interaction of albumin with a micellar solution of palmitate-1-(14)C. The radioactivities and chemical compositions of the two complexes were almost identical. Rat epididymal fat pads took up, during a 1 hr incubation, about 2.5 times as much palmitic acid from complex A as from complex B; the extent of esterification of the incorporated label was equal for the two complexes. The fractional turnover rate of palmitic acid of complex A, administered intravenously to dogs, was about twice that of palmitic acid from complex B. The label of the two complexes recirculated in the esterified fatty acid fraction of plasma to an equal extent. It is proposed that differences in the orientation of the fatty acid molecules may affect their interaction with the binding sites of albumin and that the metabolic differences of the resulting complexes are related to differences in the ease of transfer of the fatty acid from the complex to receptor sites of tissues.