detector but not by the mass spectrometer. Those compounds account for the four unidentified peaks appearing between 15 and 30 min in the absorbance chromatogram (Figure 3).The utility of reconstructed mass chromatograms is evident in Figure 4. BHT and Irganox 1076 are easily detected in the reconstructed mass chromatogram, but in the total ion current chromatogram, Irganox 1076 is obscured by the peak at scan 557.

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].

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Certain precursor proteins (APP751 and APP770) of the amyloid beta-protein (AP) present in Alzheimer's disease contain a Kunitz-type serine protease inhibitor domain (APPI). In this study, the domain is obtained as a functional inhibitor through both recombinant (APPIr) and synthetic (APPIs) methodologies, and the solution structure of APPI is determined by 1H 2D NMR techniques. Complete sequence-specific resonance assignments (except for P13 and G37 NH) for both APPIr and APPIs are achieved using standard procedures. Ambiguities arising from degeneracies in the NMR resonances are resolved by varying sample conditions. Qualitative interpretation of short- and long-range NOEs reveals secondary structural features similar to those extensively documented by NMR for bovine pancreatic trypsin inhibitor (BPTI). A more rigorous interpretation of the NOESY spectra yields NOE-derived interresidue distance restraints which are used in conjunction with dynamic simulated annealing to generate a family of APPI structures. Within this family, the beta-sheet and helical regions are in good agreement with the crystal structure of BPTI, whereas portions of the protease-binding loops deviate from those in BPTI. These deviations are consistent with those recently described in the crystal structure of APPI (Hynes et al., 1990). Also supported in the NMR study is the hydrophobic patch in the protease-binding domain created by side chain-side chain NOE contacts between M17 and F34. In addition, the NMR spectra indicate that the rotation of the W21 ring in APPI is hindered, unlike Y21 in BPTI, showing a greater than 90% preference for one orientation in the hydrophobic groove.

1. In response to electrical stimulation, the bag cell neurons of Aplysia generate an afterdischarge that lasts 20-40 min. During this afterdischarge several neuroactive peptides are released. We have now studied the time course of release of two of these peptides, egg-laying hormone (ELH) and acidic peptide (AP). For the collection of released peptides, the artery to the bag cell clusters was perfused. The medium surrounding the clusters (artificial seawater, ASW) was completely exchanged at 5-min intervals before, during, and after stimulation of an afterdischarge. Peptides released into the external medium were analyzed with the use of high-pressure liquid chromatography. 2. Before stimulation, no detectable ELH and AP were found in the external medium. After the onset of an afterdischarge, the amount of ELH and AP released increased progressively until 15-20 min of firing. Toward the conclusion of an afterdischarge, the release of ELH and AP returned to control levels. 3. In contrast to the pattern of release of the peptides, the firing rate of the bag cell neurons is maximal within the first minute of afterdischarge and thereafter declines. 4. Release of the peptides from axonal varicosities occurs within the vascularized connective-tissue sheath that covers the clusters of bag cell neurons. Experiments were therefore carried out to establish whether the observed time course of release is affected by diffusion of the peptides through the vasculature into the external medium and, in particular, to determine whether the maximal rate of release at 15-20 min into the afterdischarge could be accounted for by a delay in transport of peptides from the neurites.(ABSTRACT TRUNCATED AT 250 WORDS)

The metabolism of the methylase product inhibitor S-adenosylhomocysteine and its 7-deaza analogue S-tubercidinylhomocysteine has been studied in cultured N-18 neuroblastoma cells. The latter compound, designed to resist metabolic degradation, has been shown to be inert under the same conditions where S-adenosylhomocysteine is rapidly and extensively degraded. The product analyses elucidated by high-performance liquid chromatography indicate that the primary route of S-[8-(14)C]adenosylhomocysteine metabolism in these cells leads to adenosine. This product does not accumulate but is rapidly converted to nucleotides or oxypurines by the action of adenosine kinase and adenosine deaminase, respectively. The presence of the potent adenosine deaminase inhibitor coformycin leads to a pronounced inhibition of oxypurine formation, an increase in nucleotide formation, and a slight accumulation of the primary metabolic products adenosine and adenine.

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