The Tb-anti-ubiquitin-FK2 antibody preferentially binds to mono- or poly-ubiquitinated proteins over free ubiquitin. This antibody can be used in combination with purified GFP-substrates, fluorescein-ubiquitin, or LanthaScreen™ cell lines to develop robust high-throughput biochemical or cell based assays for ubiquitination or deubiquitination.