Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.10.3.2 (laccase)
 4,656 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The detailed nature of N-3 binding at the multi-copper active site in native laccase is investigated through a combination of low-temperature magnetic circular dichroism (LTMCD) and absorption spectroscopies. This combination of techniques allows charge-transfer spectral features associated with N-3 binding to the paramagnetic type 2 Cu(II) to be differentiated from those associated with binding to the antiferromagnetically coupled, and therefore diamagnetic, binuclear type 3 Cu(II) site. Earlier absorption titration studies have indicated that N-3 binds with two different binding constants, yielding a high-affinity and a low-affinity form. The studies presented here are interpreted as strong evidence that low-affinity N-3 bridges the paramagnetic type 2 and diamagnetic type 3 binuclear Cu(II) sites in fully oxidized laccase. This assignment is further supported by features in the MCD spectrum whose intensity correlates with an EPR signal associated with uncoupled type 3 Cu(II) sites. In these sites, N-3 has displaced the endogenous bridge, thereby rendering the site paramagnetic and detectable by both LTMCD and EPR spectroscopy. High-affinity N-3 is found to bind to the paramagnetic type 2 Cu(II) site in a limited fraction of the protein molecules that contains reduced type 3 sites. Finally, the possible role of this trinuclear (type 2-type 3) Cu(II) active site in enabling the irreversible reduction of dioxygen to water is considered.
 ...
PMID:Low-temperature magnetic circular dichroism studies of native laccase: spectroscopic evidence for exogenous ligand bridging at a trinuclear copper active site. 298 9

The multicopper oxidases contain at least four copper atoms and catalyze the four-electron reduction of O(2) to H(2)O at a trinuclear copper cluster. An intermediate, termed native intermediate, has been trapped by a rapid freeze-quench technique from Rhus vernicifera laccase when the fully reduced form reacts with dioxygen. This intermediate had been described as an oxygen-radical bound to the trinuclear copper cluster with one Cu site reduced. XAS, however, shows that all copper atoms are oxidized in this intermediate. A combination of EXAFS, multifrequency EPR, and VTVH MCD has been used to understand how this fully oxidized trinuclear Cu cluster relates to the fully oxidized resting form of the enzyme. It is determined that in the native intermediate all copper atoms of the cluster are bridged by the product of full O(2) reduction. In contrast, the resting form has one copper atom of the cluster (the T2 Cu) magnetically isolated from the others. The native intermediate decays to the resting oxidized form with a rate that is too slow to be in the catalytic cycle. Thus, the native intermediate appears to be the catalytically relevant fully oxidized form of the enzyme, and its role in catalysis is considered.
 ...
PMID:Nature of the intermediate formed in the reduction of O(2) to H(2)O at the trinuclear copper cluster active site in native laccase. 1202 53