cofactor

noun

1. A contributing factor.

   “Although many believe HTLV-III plays a primary role in the development of AIDS, it is still unresolved how the virus works and what cofactors, if any, play a role.”

2. A substance, especially a coenzyme or a metal, that must be present for an enzyme to function.
3. A molecule that binds to and regulates the activity of a protein.
4. The result of a number being divided by one of its factors.
5. The signed determinant of the submatrix produced by removing the row and column containing a specified element; primarily used in the recursive definition and calculation of the determinant of a matrix.