SUBUNIT STOICHIOMETRY OF HUMAN PROTEASOMES

Subunits from human placental proteasomes were separated by two-dimens ional polyacrylamide gel electrophoresis. The amino acid composition o f proteins from individual spots were determined. Some of the spots ha d identical amino acid compositions, confirming that they contain isof orms of the same subunit. Proteasomes from HeLa cells, labelled with H -3-leucine, were precipitated with an antibody and similarly separated into subunits. The radioactivity in each subunit was measured. The su bunit stoichiometry was then calculated from these data and the leucin e contents in the subunits. Each of the 14 major subunits of human pro teasomes are apparently present in equal amounts.