Rat FABPA associates with HSL and increases the rate of triacylglycerol hydrolysis, possibly by sequestering the released fatty acids (Shen et al. 1999; Shen et al. 2001). A similar association of HSL and FABP4 at the lipid droplet surface has been demonstrated in human adipocytes (Smith et al. 2004). The stoichiometry of the fatty acid:FABP complex is unknown. This model implies that HSL-associated FABP loaded with fatty acid should exchange with unloaded, unassociated FABP, allowing HSL to continue to work efficiently while moving newly generated fatty acids away from the lipid particle. To date, there is no evidence for or against such a shuttling process.