Which enzyme is activated by the presence of more than one metal ion?

The inhibition of succinate dehydrogenase by malonate is an example of:

Enzymatic activity is inhibited by which of the following?

Statement $P$: Enzymes are biological catalysts.
Statement $Q$: They are produced by living cells in small amounts to catalyze reactions.

Which of the following enzymes was first isolated and purified in the form of crystals?

The enzyme which converts sucrose into glucose and fructose is: