Purification and characterization of ubiquitin from mammalian testis

Ubiquitin was extracted from testis of 4 mammals and purified to homogeneity by gel filtration chromatography. Amino acid compositions and NH2-terminal sequences were found to be identical in the 4 species and with calf thymus ubiquitin. Ubiquitin conformation was shown to be very sensitive to oxidation. Improved methods for radioimmunoassay of ubiquitin in tissue extracts are also discussed.