Abstract: The present invention provides a novel method for the rapid isolation and identification of large numbers of novel enzyme substrates. The novel method provided by the present invention identifies substrates in tissue and/or cell extracts of a non-human model characterized as having an inactive enzyme. Without active enzyme, the substrates of this enzyme accumulate in the non-human model. The tissue or cell extract containing the enzyme substrate is then fractionated by passing the extract through an affinity column. The affinity column comprises an enzyme having similar specificity to the inactive enzyme, bound to a solid support. The affinity resin binds the enzyme substrate so that the substrate may be isolated from other proteins in the extract. The substrate of the enzyme may then be further identified by purifying and sequencing. Also provided by the present invention are novel substrates, and analogs of the substrates identified by the method of the present invention.