Rat HSL is inactivated by dephosphorylation. The catalyst of this reaction is unknown. Protein phosphatases 1 and 2A are both abundant in rat adipocytes and both are active on HSL (Olsson and Belfrage 1987; Wood et al. 1993). Whether these enzymes act on phosphate groups attached to serine residues 659 and 660 of HSL is unknown, however (Holm et al. 2000). Although the reaction is annotated as though the phosphatase acts on phosphorylated HSL monomers, this also is unknown: does the HSL:FABP complex dissociate before HSL dephosphorylation (as implied here), or does dephosphorylation of HSL drive dissociation of the complex?

Dephosphorylation of human HSL has not been studied in detail, so the human reaction is inferred from the well-studied rat one.