A zymoprotein is a protein that doubles as an enzyme — a protein with catalytic power. Most enzymes are proteins, so in a strict sense most enzymes are zymoproteins; the term distinguishes catalytic proteins from structural or storage proteins that have no enzymatic activity. In food science the distinction matters in contexts like egg white, where ovalbumin is a plain protein but lysozyme is a zymoprotein that attacks bacterial cell walls — contributing to the egg’s natural defences. The word belongs to the older biochemical vocabulary, when classifying proteins by function was novel. Today enzymologist will do, but zymoprotein precisely names the overlap of the two categories.