Helmut Sies and the compartmentation of hydroperoxide metabolism.

The early work of Helmut Sies on mammalian hydroperoxide metabolism is reviewed with particular emphasis on the in situ function of catalase and glutathione peroxidase1. Starting out from a catalase-dominated thinking in the middle of the last century, Sies first demonstrated, by whole organ spectroscopy, that H2O2 is generated in rat liver and metabolized by catalase. In a joined effort with the author's group, he then worked out that glutathione peroxidase can kinetically compete with catalase in hydroperoxide metabolism in situ. In compartmentalized cells, however, the "competition" of the two enzymes turned out to be a mutual complementation because of their different subcellular location. The studies for the first time documented that the metabolism of freely diffusible hydroperoxides is compartmentalized and, thus, paved the way to a better understanding of oxidant challenges and redox regulation. The article, garnished with personal memories, is meant as a nostalgic journey though ancient times of biochemistry with their changing fashions and paradigms, revealing the roots of topical perspectives and controversies in redox biology.