A major pre-P-amyloid proteinsps (APP,,,) processing activity from Alzheimer's disease brain extracts was identified and found to be indistinguishable from the activity of cathepsin D.APP,, processing activity cleaved APP,,, into a series of fragments that reacted on immunoblots to a monoclonal antibody (C286.8a) against p-amyloid-( 1 -7)-peptide and cleaved N-dansyl-APP-(591-601)-amide at the Glu-Val and Met-Asp bonds. Fragments of 5.5 kDa and 10-12 kDa were formed from the cleavage of APP,,, by cathepsin D at the Glu593-Val594 bond, and had the same Nterminus as a minor form of P-amyloid released by cells. Abbreviations. APP,,,, pre-P-amyloid protein,,, isoform; [N5", L5'6]APP,,,, APP,,, with lysine and methionine at positions 595 and 596 replaced by asparagine and leucine, respectively; dansyl, 5-(dimethylamino)-napthalene-1-sulfonyl; N-dansyl-APP-(591-601)-amide, N-dansyl-ISEVKMDAEFR-amide; C286.8a, IgG,, mAb recognizing P-amyloid residues at positions 1-7; PhMeSO,F, phenylmethylsulfonyl fluoride; E-64, trans-epoxysuccinyl-L-leucylamido(4-guanidino)butane; P-2, post-I5000 g pellet.Enzymes. Cathepsin D (EC 3.4.23.5); type I1 site-specific deoxyribonucleases (EC 3.1.21.4).-~ processing enzyme, the activity of which is influenced by a mutation associated with the Swedish pedigree of familial Alzheimer's disease. MATERIALS AND METHODSHuman cathepsin D from Calbiochem was pure by SDS/ PAGE, 93% accurate by amino acid analysis, and contained only cathepsin D derived N-termini, the majority of which were from equimolar amounts of the mature light (GPI-PEVLKNY-), and heavy (GGVKVERQVF-) chains. Pepstatin A and heparin agarose were from Sigma. Mono-Q columns were from Pharmacia. Rabbit antiserum to human cathepsin D was from Dako Corp. IgG was purified from rabbit sera using Avid AL [23] and coupled to CnBr-activated Sepharose 4B [24]. The methods and instrumentation for peptide synthesis [25], amino acid analysis [26] and mass spectrocopy [26] were as cited previously. The protein content of crude extracts was determined by the Bradford assay [27].

A murine model of disseminated candidiasis involving intranasal challenge with Candida albicans was developed and used to explore the role of C. albicans aspartic proteases as virulence factors during early dissemination. Pretreatment of neutropenic mice with the aspartic protease inhibitor pepstatin A by intraperitoneal injection afforded strong dose-dependent protection against a subsequent lethal intranasal dose of an aspartic protease-producing strain (ATCC 32354) of C. albicans. Administration of 0.6 mg of pepstatin A kg of body weight ؊1 prior to challenge and on days 1 to 4 postchallenge resulted in 100% survival at day 15 postchallenge, whereas 100% of animals receiving saline had died by day 6. This effect was comparable to the dose-dependent protection obtained with amphotericin B, which resulted in 100% survival when administered at 0.1 mg kg ؊1. The reduction in mortality afforded by pepstatin A correlated with its dose-dependent blockade of C. albicans numbers in the lungs, liver, and kidneys. By sharp contrast, no protection by pepstatin A was observed in mice challenged intravenously, and protection was markedly attenuated in mice given pepstatin A after intranasal challenge only. These data show the utility of pepstatin A in the prophylaxis of disseminated Candida infections and suggest that Candida aspartic proteases play an essential role early in dissemination.