This chapter focusses on selective biocatalytic phosphorylation reactions of metabolites. Phosphoryl group transfer reactions are of fundamental importance for living organisms and a variety of enzyme classes are involved in catalyzing these phosphorylation reactions. A large number of phosphorylases, phosphatases, and phosphotransferases/ kinases have been described as enzymes for the biocatalytic formation of new O-P- bonds, while the number of enzymes catalyzing the formation of N-P-, S-P-, and C-P-bonds is much smaller. Analytical method development, in particular separation and detection methodologies, for the direct analysis of biocatalytic phosphorylation reactions, are described as decisive steps for the assay and screening of novel phosphorylating biocatalysts, for investigating their functional properties and for process design. It is equally important for obtaining product stability data, as the areas of stability for the phosphorylated metabolites are best determined by experiments. As high-energy phosphate compounds are key players in life processes, the most important phosphate compounds are discussed in this chapter. Even though ATP is preferable in most enzymatic phosphorylation reactions, additional phosphoryl donors with varying energy level, availability, and specificity are of great interest. The stereo- and regioselectivity of phosphorylating enzymes offers benefits for the production of phosphate esters. A selection of new emerging phosphorylation reactions is shown. The subchapter on reaction engineering for biocatalytic phosphorylation processes provides basic reaction engineering principles, reaction kinetics, reaction system and process optimization strategies for biocatalytic phosphorylation reactions. The transition from stoichiometric phosphorylation reactions to biocatalytic phosphorylation reactions improves selectivity, safety, health, and environment, reduces the number of reaction steps in existing phosphoryla-tion routes, and decreases the waste-to-product ratio, if the phosphate donor is either recycled or used up in the reaction.
