FATTY-ACID DOUBLE-BOND ORIENTATION ALTERS INTERACTION WITH L-CELL FIBROBLASTS

Relatively little is known of fatty acid specificity in cellular fatty acid uptake. In this study L-cells, a fibroblastic cell line with ver y low levels of endogenous cytosolic fatty acid binding protein, were used to examine the role of cis and trans unsaturation on fatty acid u ptake. The fluorescent fatty acids, trans-parinaric acid and cis-parin aric acid, were used as analogs of straight-chain saturated, and kinke d-chain unsaturated fatty acids, respectively, in order to evaluate th e fatty acid specificity of the uptake system. Parinaric acid is poorl y metabolizable; greater than 97% was unesterified while H-3-oleic aci d was almost totally metabolized after 30 min uptake. Cis- and trans-p arinaric acid uptake was saturable and dependent on the concentration of fatty acid. However, the initial rate and maximal amount of trans-p arinaric acid taken up by the L-cells was greater than for cis-parinar ic acid under the same conditions. The affinity of L-cell uptake for t rans-parinaric acid (K-m = 0.12 uM) was 35-fold higher than that for c is-parinaric acid (K-m = 4.17 uM). Based on competition studies with o leic and stearic acids, it was concluded that the cis- and trans-parin aric acid were taken up by the same L-cell fatty acid uptake system. T he results suggest that the L-cell fatty acid uptake system has select ivity for straight chain rather than kinked chain unsaturated fatty ac ids.