Number of metal ion present in active site of Cytochrome C-oxidase is 2.

Cytochrome C-oxidase is a key enzyme in the electron transport chain that is responsible for the final step of cellular respiration, the oxidation of cytochrome C and the reduction of oxygen to water. The active site of cytochrome C-oxidase contains a number of metal ions, which play crucial roles in the enzyme's function.

1. Heme A:
One of the metal ions present in the active site of cytochrome C-oxidase is a heme A group. Heme A is a prosthetic group that contains an iron ion (Fe) coordinated to a porphyrin ring. It is responsible for the transfer of electrons during the catalytic cycle of the enzyme. The iron ion can exist in different oxidation states (Fe2+ and Fe3+) and undergoes reversible redox reactions during the electron transfer process.

2. Copper ions:
The other metal ions present in the active site of cytochrome C-oxidase are two copper ions. These copper ions are essential for the enzyme's function and are involved in the reduction of molecular oxygen to water. The two copper ions, often referred to as CuA and CuB, are arranged in a binuclear center within the enzyme.

Function of the metal ions:
The metal ions in the active site of cytochrome C-oxidase play crucial roles in the enzyme's function. The heme A group is responsible for the transfer of electrons from cytochrome C to the copper ions. It acts as a mediator, shuttling electrons between the copper ions and cytochrome C.

The copper ions, CuA and CuB, are involved in the final step of the enzyme's catalytic cycle, which is the reduction of molecular oxygen to water. They facilitate the transfer of electrons from cytochrome C to oxygen, allowing for the formation of water. The presence of two copper ions allows for efficient electron transfer and ensures the proper functioning of the enzyme.

In conclusion, the active site of cytochrome C-oxidase contains two metal ions: heme A and two copper ions (CuA and CuB). These metal ions are essential for the enzyme's function and play key roles in the electron transfer and oxygen reduction processes.