Described herein are methods, systems, and compositions for detecting enzyme activity. In some embodiments, the reaction product(s) are coupled with a mass tag, and the enzyme activity is determiner by analyzing the reaction product(s). The enzyme assays can be performed using mass spectrometry, for example nanostructure-initiator mass spectrometry (NIMS). Also described are methods, systems, and compositions for monitoring enzymatic degradation process of a substrate sample, for example a biomass.
STATEMENT GOVERNMENT RIGHTS
 This invention was made with governmental support awarded by the National Institutes of Health under Grant No. 1RC1GM090980-01, and by the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231, DE-FC02-07ER64494, and DE-AC04-94AL85000. The government has certain rights in the invention. This work is also a collaboration between inventors at Lawrence Berkeley National Laboratory and Sandia National Laboratories for the Joint BioEnergy Institute.