What is the optimal MSR for biotinylation of my protein or antibody?

The optimal biotin MSR depends on the MW of the protein. We suggest 2–3 biotins for proteins < 50 kDa, 3–4 for 60–100 kDa proteins, and 4–6 for antibodies. This has to do with the percentage of Lys residues present, and how many charges are removed (which can and will affect the protein coming out of solution).