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Metal ion mediated inhibition of firefly bioluminescence: A possibility via a quaternary complex

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Title Metal ion mediated inhibition of firefly bioluminescence: A possibility via a quaternary complex
 
Creator Sudhaharan, T
Reddy, A Ram
 
Description 256-267
D(-) Luciferin, interacts with different
metal ions to produce colourless soluble salts with absorption spectra broader,
intense and red shifted as compared to those of the parent compound. The
equilibrium constants for the luciferin-metal ion system vary in the order,
depository divalent transition metal ions > alkali metal ions. The
equilibrium constants for the ternary complexes formed between metal ions and a
mixture of lucifcrin and luciferase are larger than that of binary complexes
but vary in the same order. Steady state fluorometric titration's of luciferin
further confirmed its complexation with metal ions. The single absorption
maximum of firefly luciferase at 278 nm originating from tyrosine was split
into a doublet in presence of transition metal ions. The absorption maximum at
lower wavelength is attributed to the H-bond raptured free tyrosine denatured
conformation of the luciferase while the longer wavelength band to tyrosine-
transition metal ion complex. Difference spectra of luciferase metal ion
complex yielded change in the molar extinction coefficients from which the
number of tyrosine molecules exposed to aqueous solution by the perturbant
metal ions are evaluated following the Donovan model. The number of tyrosine
molecules exposed to the aqueous medium as a result of conformational change in
the enzyme are 4, 3, 3, 2 and 3 by Hg2+,Mn2+, Co2+,
Cd2+ and Cs+ respectively. The denaturation constants
calculated for the luciferase-metal ion complexes vary between 0.152 and 0.570
and follow the order of Hg2+> Cs+> Cd2+>
Co2+> Mn2+. Steady state fluorescence data reveal that
the metal ions quench the fluorescence of enzyme by complexation with the side
chain residues of the excited state tyro sine. Profound change in the UV CD
spectrum of luciferin and luciferase in presence of metal ions was attributed
to the conformational change in the substrate and enzyme. Thus the inhibition
of luciferase activity in the firefly bioluminescence by metal ions is
attributed to the quaternary complex formed between metal ion-luciferin-luciferase
and ATP near or around the active site of the enzyme.
 
Date 2013-07-16T08:50:28Z
2013-07-16T08:50:28Z
2000-08
 
Type Article
 
Identifier 0975-0959 (Online); 0301-1208 (Print)
http://hdl.handle.net/123456789/19831
 
Language en_US
 
Rights CC Attribution-Noncommercial-No Derivative Works 2.5 India
 
Publisher NISCAIR-CSIR, India
 
Source IJBB Vol.37(4) [August 2000]