The architecture, organization and functioning of biocatalytic reaction networks, which are coded in the cell specific genome and which work together in the small space of biological cells, are a fascinating feature of life evolved over more than 3 billion years. The knowledge about the diversity of biocatalytic functions and metabolic pathways sustaining life on our planet is highly important, especially as the currently occurring loss of biodiversity is considered a planetary boundary which is at high risk, and knowledge about the life of current biological organisms should be gained before they become extinct. In addition to the well-known enzymatic reactions involved in biochemical pathways, the enzyme universe offers numerous opportunities for discovering novel functions and pathways. Maintaining thousands of molecules and reactions functioning properly within biological cells, which may be exposed to various kinds of external hazards, environmental stress, enzymatic side reactions or non-enzymatic chemical reactions, is key for keeping cellular life healthy. This review aims at outlining advances in assigning enzyme functions to protein sequences and the discovery of novel biocatalytic functions and pathways.

Methodologies for the synthesis and purification of metabolites, which have been developed following their discovery, analysis and structural identification, have been involved in numerous life science milestones. The renewed focus on the small molecule domain of biological cells has also created an increasing awareness of the rising gap between the metabolites identified and the metabolites which have been prepared as pure compounds. Due to the large number and molecular diversity of metabolites the design and engineering of resource-efficient and straightforward synthetic methodologies for their production have attracted much interest. The variety of metabolic pathways in biological cells provide a wonderful blueprint for designing simplified and resource-efficient synthetic routes to desired metabolites. Therefore, biocatalytic systems have become key enabling tools for the synthesis of an increasing number of metabolites, which can then be utilized as standards, enzyme substrates, inhibitors or products, or for the discovery of novel biological functions.