I'm posting this reply on behalf of my colleagues from the ENZYME helpdesk - please consider writing to the helpdesk next time, where you are more likely to receive a timely reply.
ENZYME db includes all the enzymes described in the International Union of Biochemistry and Molecular Biology (IUBMB) nomenclature list, also known as the EC list (see http://www.chem.qmul.ac.uk/iubmb/enzyme/ and http://enzyme-database.org/). ENZYME was the first computer readable version of the EC list and is distinguished by its close collaboration with UniProtKB: All relevant EC entries are cross-referenced to the corresponding UniProtKB/Swiss-Prot entries, and these latter entries get their information about enzyme name and chemical reaction catalyzed directly from ENZYME.
MetaCyc also includes all the reactions described in the EC list. As MetaCyc is a Metabolic Pathway Database, the database includes additional reactions that allows to completely describe entire known pathways even though some reactions have only been partly characterized at the biochemical level.
The quality of data in both resources is high, and is documented with references to the literature which described the reaction.