molecular and active-site structure of tyrosinase
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02-UTILIZATION & PROCESSING 311
LOO9 MOLECULARAND ACTIVE-SITE SrRUcrURE OF TYPGSINASE. M.P. Jackman, M. Huber a&K. Perch. Biochemisches Institut der Universitgt
Ziirich, Winterthurerstrasse 196, CH-8057 Ziirich, Switzerland. Tyrosinase is a copper-containing monooxygenase catalyzing both
the o-hydroxylation of mmphenols and aromatic amines and the oxida- tion-of o-diphenols to o-quinones and o-aminophenols to o-quinoneimines. The acti'iTe site of the- enzyme consists of a coupled bynuclear copper center which interacts with both molecular oxygen and organic substra- tes. Spectroscopic ard protein sequencing data have shown that tyrosi- nase is structurally related to the oxygen-transporting hemocyanins. To elucidate the factors influencing oxygen and substrate binding in tyro- sinase, we have performed site-directed mutagenesis of the gene from the bacterium Streptomyces glaucescens. Chemical and spectroscopic properties of the mutant enzymes will be presented.
L(-)l() BINDING AND AC’?IVATION OF DIOXYGEN BY COPPER COMPLEXES. A. D. Zubsrbiihler, University of Basel, Basel, Switzerland. Binding and Activation of dioxygen by copper complexes has long
been based purely on kinetic evidence for low molecular systems. With the developarent and characterization (1) of quasireversible p-peroxo copper complexes it has beccrme possible to obtain the thermodynamic and kinetic parameters of dioxygen binding and oxygenation of organic substrates. Enthalpies of formation of such adducts are close to those of iron complexes and of biological dioxygen carriers, i.e. roughly 60 kJ/mol, reaction entropies being responsible for their low stability constants at room temperature. Experimental evidence is indicating a strong electrophile as the oxygenating species. Dioxygen activation occurs both thermally and photochemically.
[ll K.D. Kariin et-al., J. Am. &em. Sot., 106, 6769 (1988).
Loll Robert
SPECTROSCOPIC AND SITE-DIRECTED MUTAGENESIS STUDIES ON Cu2Zn2SOD. Lucia Banci, Ivano Bertini, Claudio Luchinat, and A. Hallewell - University of Florence, Florence, University of
3ologna Italy and Chiron Corporation, Emeryville, CA, U.S.A. Copper-zinc superoxide dismutases catalyze in vitro the reaction
of dismutation of superoxide anion and seem to have, also in vivo, a role of protection against oxygen toxicity. The catalytic mechanism for Cu2Zn2SOD is still an open
i fascinating problem. Spectroscopic
studies, particularly through H NMRD measurements, 'H NMR spectra on the fully active Cu2CO2 derivative, and site directed mutagenesis on some aminoacid residues present in the active cavity that are thought to have a key role in the enzymatic reaction (Arg-143, Thr-137, Glu-133, Glu-132, ~~~-124, Asp-1251, have shed light on the reaction mechanism. Aniosn bind copper and some of them act as inhibitors. They induce changes in the coordination polyhedron which are discussed in detail.