Protease 'Clipsin' extract activity reflects demographic characteristics of human brain

'Clipsin' and other peptide bond hydrolase activities that appear to be integral membrane proteins, including two implicated in the formation of the histological hallmarks of Alzheimer's disease, were assayed in the frontal and parietal cortex from a large (n = 45) series of postmortem human brains. Tissues were extracted sequentially with detergent-containing and low ionic strength buffers. The final extracts obtained with detergent-high ionic strength buffer were assayed for peptide-bond hydrolase activity using radiolabelled casein and four chromophore-linked peptide substrates. Hydrolysis of N-succinyl-Ala-Ala-Pro-Phe-p-nitroanilide and alpha-casein showed evidence of sensitivity to the presence of Alzheimer's disease (n = 22) and some of the seven other demographic features (postmortem delay; mode of death in the case of one substrate) of the brain samples considered. By contrast, activity towards carbobenzoxy(Z)-Leu-Leu-Glu-2-naphthylamide, Z-Val-Lys-Met-4-methyl-coumaryl-7-amide and Z-Val-Lys-Lys-Arg-4-methoxy-2-naphthylamide were independent of all factors. The results are discussed in terms of damage to a sub-population of protease-containing membranes.