Strategies for quantifying the enzymatic activities of glycoside hydrolases within cells and in vivo

Within their native milieu of the cell, the activities of enzymes are controlled by a range of factors including protein interactions and post-translational modifications. The involvement of these factors in fundamental cell biology and the etiology of diseases is stimulating interest in monitoring enzyme activities within tissues. The creation of synthetic substrates, and their use with different imaging modalities, to detect and quantify enzyme activities has great potential to propel these areas of research. Here we describe the latest developments relating to the creation of substrates for imaging and quantifying the activities of glycoside hydrolases, focusing on mammalian systems. The limitations of current tools and the difficulties within the field are summarized, as are prospects for overcoming these challenges.