Abstract
Lipases/acyltransferases are a special group of lipases with highly enhanced affinity for other nucleophiles than water compared to classical lipases. In the presence of a suitable acceptor, they catalyze acyltransfer reactions (such as alcoholysis, aminolysis, or perhydrolysis) much faster than hydrolysis even in aqueous media with a high thermodynamic activity of water (aW). This allows kinetically controlled reactions where the donor ester is fully converted into the ester product before any significant release of free fatty acids. This chapter will discuss the kinetic aspects of the competitive reactions catalyzed by lipases/acyltransferases, propose a model, and a procedure to quantify their acyltransferase character, present some applications, and give an overview of currently known lipases/acyltransferases and of the structural studies and protein engineering strategies that have aimed at further improving their catalytic properties or even at turning lipases into acyltransferases.