OPIATE ANALGESICS DUAL ROLE IN FIREFLY LUCIFERASE ACTIVITY

The effects of three opiate analgesics, isolated from opium, on the fi refly luciferase enzyme have been studied. Morphine (MN), 6-acetylmorp hine (MAM), and diacetylmorphine(DAM) inhibited the enzyme activity at different levels. At lower concentrations, MN and MAM enhanced enzyme activity, effecting inhibition at higher concentrations. However, DAM inhibited the enzyme activity at all concentrations investigated. The stimulating activity of MN and MAM is attributed to the hydrophilic i nteraction of the proton donor-acceptor type with the polar regions of the luciferase located outside the binding pocket of the active site. The inhibition at higher concentrations of MN and MAM and at all conc entrations of DAM is found to be competitive in nature, with the analg esics competing for the binding of the enzyme's natural substrate luci ferin. The binding site of the luciferase could accommodate only one a nalgesic molecule. Binding constants determined from bioluminescence s tudies showed that the inhibitor binding site is hydrophobic in nature . The inhibition constants of analgesics are in the order MN > MAM > D AM. The greater binding of DAM to luciferase is attributed to its abil ity to form a ground state complex with ATP and greater hydrophobicity . At higher concentrations of ATP, the binding constants increased. Th e results obtained are explained assuming that the firefly luciferase acts as a subtype mu-opioid receptor model.