Differences in catalytic activities and subunit pattern of multicatalytic proteinase complexes (proteasomes) isolated from bovine pituitary, lung, and liver. Changes in LMP7 and the component necessary for expression of the chymotrypsin-like activity.

Polyacrylamide gel electrophoresis and high performance liquid chromatography of multicatalytic proteinase complexes (MPC) isolated from bovine pituitary, lung, and liver showed marked differences in the pattern of subunits. The concentrations of LMP7 in the lung and liver were 10 and 5 times, respectively, greater than those in the pituitary, whereas the chymotrypsin-like activity and the amount of a subunit (BO2), necessary for its expression, were markedly decreased in the lung and moderately decreased in the liver. Lower trypsin-like, small neutral amino acid preferring, and peptidyl-glutamyl-peptide hydrolyzing activities were also found in the lung and liver. The activity of the branched chain amino acid preferring component (BrAAP), predominantly latent in the pituitary, was highly activated in the lung and liver, as evidenced by a greatly decreased Km and a 20-fold increase of the specificity constant Vmax/Km, indicating facilitated substrate access to its active site and increased affinity toward substrates with branched chain amino acids in the P1 position. It is suggested that overexpression of LMP7 in the lung is related to increased exposure of the airways to foreign antigens. The possible association between amounts of LMP7 and the activation of the BrAAP component needs further examination.