Metal ion-catalysed interaction of peroxidase with morphine and protein

Morphine Binds Creatine Kinase B and Inhibits Its Activity

Morphine is an analgesic alkaloid used to relieve severe pain, and irreversible binding of morphine to specific unknown proteins has been previously observed. In the brain, changes in the expression of energy metabolism enzymes contribute to behavioral abnormalities during chronic morphine treatment. Creatine kinase B (CK-B) is a key enzyme involved in brain energy metabolism. CK-B also corresponds to the imidazoline-binding protein I₂ which binds dopamine (a precursor of morphine biosynthesis) irreversibly. Using biochemical approaches, we show that recombinant mouse CK-B possesses a μM affinity for morphine and binds to morphine in vitro. The complex formed by CK-B and morphine is resistant to detergents, reducing agents, heat treatment and SDS-polyacrylamide gel electrophoresis (SDS-PAGE). CK-B-derived peptides CK-B_1–75 and CK-B_184–258 were identified as two specific morphine binding-peptides. In vitro, morphine (1–100 μM) significantly reduces recombinant CK-B enzymatic activity. Accordingly, in vivo morphine administration (7.5 mg/kg, i.p.) to mice significantly decreased brain extract CK-B activity compared to saline-treated animals. Together, these results show that morphine strongly binds CK-B and inhibits its activity in vitro and in vivo.

Comparison of the interaction of tricyclic antidepressants with human polymorphonuclear leukocytes as monitored by the generation of chemiluminescence

The interation of imipramine with human polymorphonuclear leukocytes (PMNs) results in a chemiluminescence (CL) response which has been attributed to the electronic excitation of the imipramine molecule resulting from a reaction of the drug with reactive oxygen species. In order to determine what portion of the tricyclic molecule is involved in this reaction, the interaction of other tricyclics with PMNs was monitored by chemiluminescence. It was observed that tricyclic antidepressants having a carbon atom at position 5 of the ring moiety (amitriptyline, for example) did not yield CL with either resting or zymosan-activated PMNs. In fact this group of compounds inhibited the zymosan-induced CL response. However, CL was observed, with both resting and metabolically-activated PMNs, from several tricyclics having a heterocyclic nitrogen at position 5. These included imipramine, desipramine, opipramol and iprindole. Chlorimipramine, which has a chlorine atom at position 3 of the ring system, failed to yield CL with resting or stimulated cells. Similarly, imipramine N-oxide failed to yield CL with resting cells, but enhanced CL was observed with zymosan-activated PMNs. On the basis of these observations it appears that some aspect of the ring moiety, other than just a heterocyclic nitrogen, facilitates a reaction between these molecules and reactive oxygen which culminates in the generation of CL.