Protein labelling with 3H-NSP (N-succinimidyl-[2,3-3H]propionate)

A tritium compound with low molecular weight and diameter, N-succinimidyl-[2,3-3H]-propionate (3H-NSP), was used to label histones and nonhistone proteins from calf thymus, and nuclear and total salivary gland proteins from larvae of the midge Chironomus thummi. Labelled proteins were visualized after electrophoresis in 10% polyacrylamide slab gels by fluorography. The method is much more sensitive than staining procedures, allowing to discern approx. 0.1 microgram protein.