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Biomedical subjects

F Ashall

Publications and source records attributed to F Ashall.

At least 19 recordsLinked to original sources
PubMed1998

Molecular pathogenesis of sporadic and familial forms of Alzheimer's disease.

Our understanding of the pathogenesis of Alzheimer's disease (AD) comes primarily from the study of rare inherited forms of the disease. Mutations that cause familial AD appear to act by a common mechanism: that of increasing production of A beta 42/43, one of the family of A beta peptides deposited in senile plaques. However, increased A beta 42/43 production has not been demonstrated to occur in most cases of sporadic AD, suggesting that genetic and environmental factors acting at other stages of the disease process can modify the risk for disease. Such factors most likely include those affecting A beta aggregation or clearance, the inflammatory response, cerebrovascular disease, or susceptibility of neurons to injury. Identifying these factors will lead to a better understanding of the etiology of the disease and provide additional targets for therapeutic intervention.

Age of Onset↗
PubMed1997

Exploring the etiology of Alzheimer disease using molecular genetics.

Alzheimer disease (AD), the most common cause of dementia in the elderly, exists in both familial and sporadic forms. Genetic studies have led to the identification of 3 genes, beta-amyloid precursor protein (APP), presenilin-1 (PS1), and presenilin-2 (PS2), which, when mutated, can cause familial forms of AD. Mutations in each of these genes result in elevated levels of A beta42/43, a proteolytic processing fragment of APP that is deposited in brains of AD patients. Transgenic mice carrying AD-causing mutations in APP develop spontaneous age-related beta-amyloid (A beta) deposition and memory impairment. Genetic linkage and association studies have also shown that the epsilon4 allele of the apolipoprotein E (APOE) gene increases risk for AD in a dose-dependent manner in both familial and sporadic forms of AD and may account for as much as 50% of the attributable risk. APOE genotyping may be useful both as an adjunct to diagnosis and in identifying patient groups for therapeutic intervention. While the biological basis for the association of APOE epsilon4 with AD is not known, age of onset and A beta deposition are positively correlated with epsilon4 allele dosage in some cases, suggesting that this risk may also be mediated directly or indirectly through A beta. Because 50% of AD cases have no APOE epsilon4 alleles and families showing mendelian inheritance of AD exist in whom there are no mutations in any of the APP, PS1, or PS2 genes, it is likely that there are additional AD risk factors, both genetic and environmental, still to be identified.

Aged↗
PubMed1994

The major secreted product of the whipworm, Trichuris, is a pore-forming protein.

The data presented here describe the first unequivocable characterization of a pore-forming protein in any helminth parasite. The excretory/secretory (E/S) material of the human whipworm T. trichiura contains a highly abundant protein of molecular mass 47 kDa (TT47); the murine model parasite, T. muris, contains a similarly abundant protein of molecular mass 43 kDa (TM43). When purified to homogeneity, these proteins induce ion-conducting pores in lipid bilayers. Antibodies raised against TM43 abolish channel activity. Pore formation in epithelial cell membranes may facilitate invasion of the host gut by Trichuris and enable the parasite to maintain its syncytial environment in the caecal epithelium. The observation that this activity may be inhibited by antibody opens a possible avenue for drug and vaccine development.

Animals↗
PubMed1994

Role of the beta-amyloid precursor protein in Alzheimer's disease.

Deposition of beta-amyloid peptide in the brain is an early event in Alzheimer's disease, the most common cause of dementia. Studies of the beta-amyloid precursor protein (APP), which gives rise to beta-amyloid, are rapidly leading to a better understanding of the biochemical basis of the disease--a prerequisite for rational drug development.

Aged↗
PubMed1994

Characterization of peptidases of adult Trichuris muris.

Excretory/secretory (E/S) material of Trichuris muris was found to contain 2 major peptidases, M(r) 85 and 105 kDa, which degrade gelatin optimally at pH 6.0 in sodium dodecyl sulphate-polyacrylamide gels. The peptidases were inactivated by diisopropylfluorophosphate, leupeptin and soybean trypsin inhibitor, but were unaffected by inhibitors of aspartic-, cysteine- and metallo-peptidases, indicating that they are serine peptidases. Both enzymes were detectable within 5 h after incubation of worms in culture medium and showed a time-dependent increase in levels. Neither peptidase was detected in worm extracts, suggesting that they are activated during or following secretion from worms. Live worms degraded a radio-isotope labelled extracellular matrix protein substratum derived from mammalian cells. Aminopeptidase activities capable of catalysing hydrolysis of amino acyl aminomethylcoumarin (MCA) substrates and a Z-Phe-Arg-MCA-hydrolysing cysteine peptidase activity, were detected in extracts of adult worms but not in E/S material.

Amino Acid Sequence↗
PubMed1992

Protease activities in carp retina.

Protease of carp retina were examined by electrophoresis and fluorogenic assays. A 70 kD serine protease with an alkaline pH optimum was detected in gelatin-containing polyacrylamide gels. A similar enzyme was found in carp brain and muscle, but not in lens. Using aminomethylcoumarin (MCA) substrates, activities that hydrolysed Z-Phe-Arg-MCA, Boc-Ala-Gly-Pro-Arg-MCA and various aminoacyl-MCAs were detected. The Z-Phe-Arg-MCA hydrolase was an acidic cysteine protease, whereas the Boc-Ala-Gly-Pro-Arg-MCA hydrolase was an alkaline cysteine protease. All aminoacyl hydrolase activities tested were inhibited by bestatin and o-phenanthroline, but not by inhibitors of serine, cysteine and aspartic proteases, suggesting they are metalloaminopeptidases. Of the substrates tested, Tyr-MCA was the most readily hydrolysed aminoacyl substrate. Preliminary evidence was obtained suggesting that levels of these activities do not differ between light- and dark-adapted retinae. The proteases have a potential involvement in retinal functioning and show similarities to other proteases known to act in the central nervous system. In particular, the Tyr-MCA hydrolase may be related to an enzyme known to remove the N-terminal tyrosine residue from enkephalin.

Amino Acid Sequence↗
PubMed1992

Detection of peptidases in Trypanosoma cruzi epimastigotes using chromogenic and fluorogenic substrates.

Detergent extracts of Trypanosoma cruzi epimastigotes catalysed the hydrolysis of a range of amino-acyl and peptidyl p-nitro-anilides and aminomethylcoumarins. At least three enzymes were detected that cleave Z-Phe-Arg-MCA. Two of these were optimally active at alkaline pH, the other at pH 4.0. Of the two enzymes with alkaline pH optima, one was a cysteine peptidase and was unable to cleave Bz-Arg-MCA readily, whilst the other cleaved Bz-Arg-MCA and was inhibited by diisopropyl fluorophosphate. The acidic enzyme was similar to cathespin L of other eukaryotes with respect to its pH profile, substrate-specificity and inhibitor-sensitivity. Evidence was presented that epimastigotes contain a cysteine-type dipeptidyl aminopeptidase, one or more aminopeptidases, and a serine peptidase that cleaves Boc-Ala-Ala-pNA. Digitonin solubilization of the activities from cells supports the hypothesis that the cathespin L-like enzyme and the dipeptidyl aminopeptidase are lysosomal, whilst the Bz-Arg-MCA hydrolase, the aminopeptidases and the Boc-Ala-Ala-pNA serine peptidase are cytosolic.

Amino Acid Sequence↗
PubMed1991

Patent confusion.

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Patents as Topic↗
PubMed1991

Characterization of proteolytic enzymes from larval and adult Nippostrongylus brasiliensis.

Proteases from infective larval (L3) and adult stages of Nippostrongylus brasiliensis were investigated with a combination of techniques involving gelatin degradation and cleavage of fluorogenic substrates. Analysis of L3 excretory-secretory (ES) products revealed enzymes of Mr 51, 58, 79, approximately 150 and approximately 250 kDa. Inhibition profiles indicate that the major 51 kDa protease is a metallo-enzyme. Significantly, little activity was present in larval somatic extracts, suggesting the synthesis of zymogens or precursor forms prior to secretion. Adult ES contained a distinct enzyme, of 50 kDa, and a number of other proteases were detected in somatic extracts of this stage, ranging from 51 to greater than 300 kDa. The largest of these adult somatic enzymes is also a putative metallo-protease. While nearly all enzymes from both L3 and adult are heat labile, incubation at 100 degrees C generated a previously unobserved activity at 20 kDa. Furthermore, a protease of similar size may be found in uninfected rat intestinal tissue, suggesting specific uptake of a host-associated enzyme by the parasite in the form of an inactive, heat-labile complex.

Animals↗
PubMed1990

Substrate specificity and inhibitor sensitivity of a trypanosomatid alkaline peptidase.

An alkaline peptidase of Trypanosoma cruzi and Crithidia fasciculata, previously shown to cleave on the carboxyl side of arginine and lysine residues, was examined for its ability to cleave various fluorogenic substrates and for its sensitive to peptidase inhibitors. The enzyme of both T. cruzi and C. fasciculata has a preference for cleavage of substrates with basic amino acids at the P2 as well as the P1 position of the peptide chain. Arginine and lysine are equally acceptable at P2, whereas the enzyme prefers arginine to lysine at P1. An influence of the P3 amino acid residue on substrate cleavability was also apparent. The peptidase was highly susceptible to inactivation by peptidylfluoromethanes, peptidyldiazomethanes and peptidylsulphonium salts that contained arginine or lysine at P1. Additionally, diisopropylfluorophosphate inhibited the enzyme, whereas trans-epoxysuccinylleucylamido(4-guanidino)butane and iodoacetic acid were relatively weak inhibitors. Various reversible inhibitors of the enzyme were also examined. Inhibition by members of the primary aliphatic amine series, methylamine to n-heptylamine, showed a peak of inhibition at n-butylamine, which most closely resembles the lysine side chain. Agmatine, which resembles the arginine side chain, also strongly inhibited the peptidase. The kinetics of inhibition by these basic compounds were of the competitive type. Pentamidine and hirudonin, which resemble two arginine side chains joined together, were more effective inhibitors of the trypanosomatid peptidase than bases resembling only one arginine or lysine side chain.

Amines↗
PubMed1990

Lysis of trypanosomes by peptidyl fluoromethyl ketones.

Peptidyl fluoromethyl ketones, improved reagents for inactivating cysteinyl and serine proteinases, have provided unexpected results when applied to intact trypanosomes. A lethal effect was observed but limited to the infectious phase of the parasitic growth cycle. Since the inhibitors are known only to act on proteases, the result implies the existence of a protease of critical importance during the infectious phase. A labelled inhibitor, Cbz-Ala-[3H]Phe-CH2F, indicated that the killing effect correlated with the labelling of a 68 kd protein in the trypomastigotes which we deduce is an essential protease.

Animals↗
PubMed1990

Inhibition of intraerythrocytic development of Plasmodium falciparum by proteinase inhibitors.

A group of inactivators of cysteinyl proteinases which function by covalent bond formation have been examined for their ability to inhibit the development of Plasmodium falciparum within red blood cells. The most effective of these caused inactivation of the parasite near 10(-8) M concentration. The range of inhibitory action varied with peptide structure in a manner characteristic of affinity labels for proteinases suggesting that the target of inhibition was an unidentified proteinase, probably of the cysteinyl type, but different from cathepsins B and L.

Animals↗
PubMed1990

Characterisation of an alkaline peptidase of Trypanosoma cruzi and other trypanosomatids.

A peptidase activity was purified from extracts of Trypanosoma cruzi on the basis of its ability to cleave benzoyl-arginine-p-nitroanilide. The enzyme was considered to be a cysteine-type peptidase with unusually low sensitivity to E-64. It has a pH optimum of about 8.0 for p-nitroanilides, and cleaves peptide bonds on the carboxyl side of arginine and, to a lesser extent, lysine residues. Cleavage of different substrates occurred at rates that were determined by their catalytic constants (kcat): the peptidase had the same Michaelis constant (about 30 microM) for all substrates tested. Evidence is presented that the peptidase is the major cysteine peptidase in T. cruzi extracts that cleaves p-nitroanilides next to basic amino acid residues at pH 8. The enzyme was detected in all stages of the life cycle of T. cruzi. Furthermore, evidence is presented, based on pH optima, inhibitor sensitivity, substrate specificity and kinetics, and electrophoretic mobility, that a similar or identical enzyme occurs in fifteen other species of trypanosomatid.

Animals↗
PubMed1990

Trypanosoma cruzi glycosomal glyceraldehyde-3-phosphate dehydrogenase does not conform to the 'hotspot' topogenic signal model.

The genes which encode glycosomal glyceraldehyde-phosphate dehydrogenase (gGAPDH) of Trypanosoma cruzi are arranged as a tandemly repeated pair on a single chromosome and are identical at the level of nucleotide sequence. They are separated by an intergenic region which contains a 317 base pair sequence with the properties of a retroposon. The genes express a 1.5 kb mRNA and a 38 kd protein. The amino acid sequence contains features characteristic of glycosomal enzymes such as peptide insertions and a C-terminal extension. However, T. cruzi gGAPDH lacks one of the positively charged 'hotspot' motifs which have been proposed as topogenic signals for import into the glycosome, a unique microbody-like organelle. Molecular modelling of the T. cruzi and T. brucei enzymes suggests that neither structure would fulfil the requirements of the 'hotspot' glycosomal import model.

Amino Acid Sequence↗