On the multiplicity of the enzyme catalase in mammalian liver

The literature on the complex multiplicity of mammalian catalase and the nature of the epigenetic modifications undergone by this enzyme has been reviewed, along with relevant comment on the subcellular localization and biological role of the enzyme. The epigenetic causations of multiplicity are established as being multifactorial and include oxidoreductive conversions of sulphydryl groups, the covalent attachment of carbohydrate, and partial proteolysis of the enzyme. Each of these epigenetic transformations may give rise to sets of multiple forms, and overlaps between these separate sets may give rise to extremely complex multiplicity patterns. It is concluded that any interpretation of catalase multiplicity which places emphasis on a single epigenetic causation is not compatible with the scope and variety of the available data on this enzyme. Instead, a holistic approach is urged - one giving due emphasis to the multiple causation of catalase multiplicity, and the interrelationships of these causations in the cellular situation. Rather than viewing the multiplicity of this enzyme as merely a series of interesting chemical modifications, emphasis is directed towards the fact that catalase heterogeneity provides a sensitive indication of the functional variations which occur within separate compartments of the subcellular structure, and hence becomes an essential element in any satisfactory understanding of the role of this enzyme in cellular processes.