Two-step bioorthogonal activity-based proteasome profiling using copper-free click reagents: A comparative study

The development and application of bioorthogonal two-step labeling techniques receives much attention. Employing bifunctional proteasome probe 2 the efficiency of two-step labeling of recently published biotinylated cyclooctynes 3–5 is compared to Staudinger–Bertozzi ligation in cell extracts and living cells. While cyclooctynes 3–5 react faster and at a much lower concentration then the Staudinger–Bertozzi benchmark, background labeling is considerable with these reagents.