Why Is Catalase So Fast? A Preliminary Network Hypothesis for the Rapid Enzyme-catalysed Decomposition of Hydrogen Peroxide
Lionel R. Milgrom1*
1School of Human Sciences, London Metropolitan University, 166-220 Holloway Road, London N7 8DB, UK
*Correspondence E-mail: milgromlr27412@gmail.com
Key Words: Catalase; hydrogen peroxide disproportionation; hydrogen-bonded networks; colligative properties; exclusion zones (EZ).
Received May 10th 2015; Revised Oct 12th; Accepted March 1st 2016; Published April 15th; Online April 28th, 2016
Abstract
Catalases are some of the most efficient enzymes known, disproportionating hydrogen peroxide (H2O2) to water and oxygen at rates of around tens of millions of molecules per second. Conventional biochemistry suggests a random diffusion-limited mechanism in which H2O2 molecules make their way from the external aqueous milieu, down channels from the enzyme surface, to the active sites where they are disproportionated at an extremely rapid rate.
Here, an alternative mechanism for the efficiency of catalase action is proposed, which at the same time does not contradict its known enzyme biochemistry. Catalase proteins are envisaged as epicentres of an extended network of hydrogen-bonded water and H2O2 molecules, stretching out from beyond the enzymes’ active sites, into the external cellular aqueous milieu. Consequently, as catalase functions, it provides a coherent oxidative ‘pulse’ to the H-bonded network that effectively ‘unzips’ H2O2 molecules into water and oxygen as far as it extends from the enzyme.
Such a mechanism predicts that most catalase H2O2 disproportionation should be occurring external to the enzyme. An experimental protocol is proposed, using immobilised catalase and the chemiluminescent reagent luminol, which if successful, would suggest (at least as far as catalase is concerned) some re-evaluation of the reductionist framework of enzyme reaction mechanisms involving just random molecular collisions.