1-fluoro-2, 4-dinitrobenzene modifies a tyrosine residue when it inactivates the bovine mitochondrial F(1)-ATPase

Intact fat cells incubated in the absence of epinephrine showed no detectable level of hormone-sensitive lipase (HSL) activity, whilst mechanical disruption of the cells caused an immediate HSL-catalyzed lipolytic process. This in vitro effect, along with the rapid deactivation of epinephrine-activated HSL in cell-free extracts, question the validity of equating HSL activity as assayed in broken-cell preparations with the actual lipolytic levels in intact cells.