As a result of its involvement in a reaction, an enzyme
is used up
loses energy
loses a phosphate group
permanently alters its shape.
is unchanged

As a result of its involvement in a reaction, an enzyme is unchanged.

Enzymes are catalysts that speed up chemical reactions that occur within the biological systems (they increase the reaction rate by lowering its activation energy). Enzymes react with substrate that binds to them (key-lock mechanism) and convert the substrate into the product. Most of enzymes are proteins by their structure but a few are catalytic RNA molecules-ribosymes.

Enzyme activity can be affected by other molecules (activators and repressors), pH, temperature etc.