When Did Two Genes Switch Their Function During Evolution?

Question

[Pappu]

Two known genes are involved in two separate functions in prokaryotes. But their homologs in eukaryotes are doing just the opposite functions. So my question is how to find out when and how the switch of functions of these genes happened in evolution.

[Neilfws]

Please make this question more specific, or it will be closed. It is too brief, vague and difficult to understand.