Human lymphoblast and erythrocyte multicatalytic proteases: differential peptidase activities and responses to the 11S regulator.

The multicatalytic protease (MCP) or 20S proteasome was purified from human red blood cells and two lymphoblastoid cell lines, 721.45 which constitutively expresses protease subunits LMP2 and LMP7, and 721.174 in which genes for these subunits are deleted. Each MCP was assayed using a series of fluorogenic peptides. The hydrophobic peptides gGGF-MCA, sRPFHLLVY-MCA and sLY-MCA were particularly good substrates for 721.45 MCP as compared to the enzyme from 721.174 and red blood cells. In addition, hydrolysis of gGGF-MCA and sLY-MCA was activated by human red blood cell and recombinant regulators to a greater extent using MCP from 721.45 lymphoblasts. Thus, LMP2/LMP7 and regulator appear to act synergistically in the enhanced degradation of gGGF-MCA and sLY-MCA by the multicatalytic protease.