Enzymes that are secreted in the active state are called zymase. Tylin is a zymase enzyme. Enzymes that are secreted in inactive form are called zymogens. The inactive enzyme is converted to active enzyme in the presence of some metal ions. Enzyme activity increases in the presence of metal ions are called metal activators. Activating metals are – Mn++, K+, Mg++, Ca++, Zn++ etc. Pepsinogen and trypsinogen are enzymes of zymogen nature.