OxyFile #126


T. Ramasarma
Biochemica et Biophysica Acta, 694 (1982) 69-93
From pages 70-71

I. Introduction

Knowledge of the generation of H2O2 in cellular oxidations has existed 
for many years.  It has ben assumed that H2O2 is toxic to cells and 
the presence of catalase is indicative of a detoxication mechanism.  
Other radicals of oxygen were recently recognized to be more potent 
destructive agents of biological material than H2O2.  Also catalase 
and other peroxidases utilize H2O2 in some cellular oxidation 
processes leading to several important metabolites.  Thus, the 
generation of H2O2 in cellular processes seems to be purposeful and 
H2O2 can not be dismissed as a mere undesirable byproduct.  Biological 
formation of H2O2 is not limited to the previously known flavoprotiens 
and some copper enzymes, but other redox systems, particulrly heme and 
non-heme iron proteins, are now found to undergo auto-oxidation 
yeilding H2O2.  The capacity for generation of H2O2 is now found to be 
widespread in a variety of organisms and in the organelles of the 
cells.  The reduction of oxygen to H2O by mitochondrial cytochrome 
oxidase beingthe predominant oxygen-utilizing reaction had 
overshadowed the importance of the quantitatively minor pathways.  

Under aerobic conditions generation of H2O2 by a variety of 
biomembranes has now been found to be a physiological event 
interlinked with phenomena such as phagocytosis, transport processes 
and thermogenesis in some as yet unidentified way.  The underlying 
mechanisms of of these processes seem to involve generation and 
utilization of H2O2 in mitichondria, microsomes, peroxisomes or plasma 
membranes.  This review gives an account of the potential of the 
biomembranes to generate H2O2 and its implication in the cellular