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A J Barrett

Publications and source records attributed to A J Barrett.

At least 199 records · Page 11Linked to original sources
PubMed1990

Interactions of papaya proteinase IV with inhibitors.

Papaya proteinase IV (PPIV) is not inhibited by chicken cystatin, or human cystatins A or C, unlike most other proteinases of the papain superfamily. The enzyme inactivates chicken cystatin and human cystatin C by limited proteolysis of the glycyl bond previously shown to be involved in the inhibitory inactivity of the cystatins, but has no action on cystatin A. Contamination of commercial crystalline papain with PPIV accounts for the limited proteolysis of cystatins by 'papain' reported previously. PPIV is slowly bound by human alpha 2-macroglobulin. The enzyme is irreversibly inactivated by E-64, and by peptidyl diazomethanes containing glycine in P1 and a hydrophobic side-chain in P2. The reaction of PPIV with iodoacetate is extremely slow. PPIV is inhibited by peptide aldehydes despite the presence of bulky sidechains in P1, suggesting that these reversible inhibitors do not bind as substrate analogues.

Binding Sites↗
PubMed1990

Selective cleavage of glycyl bonds by papaya proteinase IV.

The specificity of papaya proteinase IV (PPIV) has been examined with small substrates and a protein. With both classes of substrate, the enzyme shows a marked selectivity for cleaving glycyl bonds. Boc-Ala-Ala-Gly-NHPhNO2 is a convenient substrate for routine assays that discriminate well against chymopapain, the most common contaminant of PPIV. Sixteen cleavage points in beta-trypsin were identified, of which 13 are glycyl bonds. Tentative suggestions are made as to the reasons for lack of cleavage of some other glycyl bonds. The structure of PPIV has been modelled on that of papain, and we suggest that the replacement of the highly conserved residues Gly-65 and Gly-23 by arginine and glutamic acid, respectively, can account for the specificity of PPIV.

Amino Acid Sequence↗
PubMed1990

Evolution of proteins of the cystatin superfamily.

We have examined the amino acid sequences of a number of proteins that have been suggested to be related to chicken cystatin, a protein from chicken egg white that inhibits cysteine proteinases. On the basis of statistical analysis, the following proteins were found to be members of the cystatin superfamily: human cystatin A, rat cystatin A(alpha), human cystatin B, rat cystatin B(beta), rice cystatin, human cystatin C, ox colostrum cystatin, human cystatin S, human cystatin SA, human cystatin SN, chicken cystatin, puff adder cystatin, human kininogen, ox kininogen, rat kininogen, rat T-kininogens 1 and 2, human alpha 2HS-glycoprotein, and human histidine-rich glycoprotein. Fibronectin is shown not to be a member of this superfamily, and the c-Ha-ras oncogene protein p21 (Val-12) probably is not a member also. It was convenient to divide members of the superfamily into four types on the basis of the presence of one, two, or three copies of cystatin-like segments and the presence or absence of disulfide bonds. Evolutionary dendrograms were calculated by three methods, and from these we have constructed a scheme depicting the sequence of events in the evolution of these proteins. We suggest that about 1000 million years ago a precursor containing disulfide loops appeared, and that all disulfide-containing cystatins are derived from this. We follow the evolution of the proteins of the superfamily along four main lineages, with special attention to the part that duplication of segments has played in the development of the more complex molecules.

Amino Acid Sequence↗
PubMed1990

An alternative quenched fluorescence substrate for Pz-peptidase.

7-Methoxycoumarin-3-carboxylyl-Pro-Leu-Gly-Pro-D-Lys(2,4-dinitr oph enyl) is introduced as a new quenched fluorescence substrate for assaying Pz-peptidase (also known as soluble metallo-endopeptidase and endo-oligopeptidase). The value of Km for partially purified Pz-peptidase from rat muscle was 8.6 microM. High protein concentrations did not interfere with the assay, so that for the first time continuous assays of Pz-peptidase in crude tissue extracts became possible.

Amino Acid Sequence↗
PubMed1990

Recombinant interleukin 2 for acute myeloid leukaemia in first complete remission: a pilot study.

We treated nine patients in first remission from AML with rhIL-2. The toxic effects of rhIL-2 infusion were, malaise, pyrexia, and hypotension, which resolved rapidly on cessation of rhIL-2 infusion. No patient required transfer to an intensive care unit. Following rhIL-2 infusions patients developed eosinophilia, and a modest lymphocytosis, involving both NK cells, and T lymphocytes. Relapse occurred in six patients at a median of 39 weeks from remission. A particular concern was rapid relapse in the two patients with AML FAB type M5. There was no survival advantage from rhIL-2 treatment when compared to a similar group of chemotherapy only treated AML patients from this institution.

Actuarial Analysis↗
PubMed1990

The effect of tissue and cellular pH on the selective biodistribution of porphyrin-type photochemotherapeutic agents: a volumetric titration study.

Volumetric titration of aqueous solutions of haematoporphyrin IX (HP) yields two inflexion points, whereas four pK values can be obtained via mathematical fitting of the experimental data. Assignment of all pK protonation sites is made. A zwitterion is proposed as the neutral species of HP. Evaluation of the pK values of HP in the presence of sodium dodecyl sulphate (SDS) leads to a drastically altered ionic species distribution. On the basis of the distribution diagrams obtained, a pH-sensitive twofold mechanism is proposed for the selective biodistribution of porphyrin-type photochemotherapeutic agents, one involving tissue distribution and the other involving cell membrane penetration by the neutral zwitterion.

Acid-Base Equilibrium↗
PubMed1990

Thrombocytopenia after bone marrow transplantation for leukaemia: changes in megakaryocyte growth and growth-promoting activity.

Megakaryocyte growth-promoting activity (MK-GPA) was scored on a scale of 0-3 in the serum of 23 patients up to 120 d following bone marrow transplantation (BMT) for leukaemia. Nine of 19 allografts and two of four autografts had thrombocytopenia requiring platelet transfusion more than 30 d after BMT. There was a close correlation between MK-GPA and platelet count. MK-GPA reached a maximum before day 30 after BMT but remained elevated in patients with persisting thrombocytopenia secondary to poor engraftment, graft-versus-host disease (GVHD) or relapse. Recent platelet transfusion did not suppress serum MK-GPA. Two of four patients undergoing autologous BMT for acute myeloid leukaemia (AML) showed delayed platelet recovery and persistence of MK-GPA in the serum. Seven further AML remission marrows were tested for megakaryocyte production before or after autologous BMT, using pooled sera with known MK-GPA activity. Megakaryocyte generation was reduced before BMT and absent in post transplant samples. This failure of MK production was not corrected by T-cell depletion or by the presence of adherent cells from normal marrow. We conclude that thrombocytopenia after BMT is associated with an appropriate increase in MK-GPA levels in response to a reduction in the megakaryocyte pool rather than the platelet pool, and that persisting thrombocytopenia after autologous BMT is due to decreased numbers of available megakaryocyte precursors.

Adolescent↗
PubMed1990

Interleukin-2 treatment-associated eosinophilia is mediated by interleukin-5 production.

During a trial using recombinant human interleukin-2 (rhIL-2) immunotherapy for acute myeloblastic leukaemia (AML) in remission, eosinophilia was observed in all patients. We used in-vitro clonogenic assays to investigate the mechanism of the eosinophilia in five patients. The mean eosinophil count increased from 0.05 x 10(9)/l before rhIL-2 to 0.98 x 10(9)/l within 48 h of stopping the infusion, and an exponential correlation between the pretreatment lymphocyte CD4:CD8 ratio and the maximum eosinophil count was observed. RhIL-2 did not stimulate eosinophil colony formation by normal bone marrow. However, serum collected from patients during rhIL-2 infusion was a potent stimulator of eosinophil colony forming units (CFU-Eo), but had no significant stimulatory effect on granulocyte-macrophage colony forming units (CFU-GM). The CFU-Eo stimulation by pre-treatment serum was 2.8-fold higher than control serum. Serum collected during treatment stimulated CFU-Eo 12 times more than control serum (P less than 0.05). By pre-incubating patient serum, collected during rhIL-2 treatment, with monoclonal antibodies to murine IL-5, or human granulocyte-macrophage colony stimulating factor (GM-CSF), a reduction of 80% and 38% respectively in eosinophil and GM colony production was found. The CFU-Eo stimulating effect of patient serum was in the range of the CFU-Eo stimulating effect of normal serum, after the addition of 5 u/ml of recombinant murine IL-5. The results suggest that eosinophilia was caused by IL-5 and GM-CSF production by rhIL-2 stimulated CD4 positive lymphocytes. The location on chromosomes 5 of the genes for IL-5, GM-CSF and IL-3 may be associated with regulation of expression, by a common mechanism, of all the factors known to be involved in eosinophil production. This mechanism may be activated by IL-2 stimulation. The separate location on chromosome 17 of the G-CSF gene may explain the ability of IL-2 to produce a distinct stimulus to eosinophil but not neutrophil production.

Adult↗
PubMed1990

Physical and laboratory characteristics of heterozygote carriers of the Fanconi aplasia gene.

Fanconi anaemia (FA) is a recessively inherited disorder associated with a typical physical appearance and a spectrum of clinical and laboratory characteristics. Parental heterozygotes of FA patients are superficially normal in appearance and lack overt laboratory abnormalities. Furthermore, they are indistinguishable from normal subjects on chromosome analysis. In order to determine if any of the clinical or laboratory abnormalities seen in FA patients were detectable to a lesser degree in heterozygotes, we carried out detailed skeletal measurement and laboratory investigation on 16 obligate FA heterozygotes and compared the results with 40 normal control subjects. Skeletal proportions in FA heterozygotes showed significant differences from normal subjects in the ratio of the height to the inter-acromial distance (p less than 0.001), and in having significantly shorter forearms (p less than 0.05). Apart from two patients with presumed iron deficiency, haemoglobin levels were normal, but three patients showed neutropenia (less than 1.5 X 10(9)/l). Foetal haemoglobin measurements were significantly higher (p less than 0.01) and natural killer cell subsets lower (p less than 0.05) in heterozygotes. Significantly reduced mitogenetic responses to phytohaemagglutinin and interleukin-2 of peripheral blood lymphocytes in heterozygotes was also demonstrated. These results suggest that heterozygotes show minor physical and haematological abnormalities consistent with partial expression of the Fanconi gene in the heterozygote.

Adult↗
PubMed1990

Interleukin-2 inhibits growth of fibroblasts derived from human bone marrow.

The adherent layer that forms in human bone marrow suspension cultures contains fibroblast colonies which arise from colony-forming cells (CFU-F). We have demonstrated that recombinant interleukin-2 (r-IL2) inhibits growth of CFU-F by preventing their entry into S phase. This inhibition is not mediated by gamma-interferon, nor by T lymphocytes, and can be abrogated by anti-IL2 receptor antibody. r-IL2 may influence haematopoiesis by its effect on bone marrow CFU-F.

Biological Factors↗
PubMed1990

The preparation of fully active chymopapain free of contaminating proteinases.

Chymopapain (EC 3.4.22.6) was purified from commercially available dried latex of papaya (Carica papaya) by extraction at acidic pH, cation-exchange chromatography and active site-directed affinity chromatography on immobilized alanyl-phenyl-alaninaldehyde semicarbazone, with elution by mercuric chloride. The product was found by immunoassay to be essentially free of the other cysteine proteinases from papaya, including papaya proteinase IV, and was fully active. The rate of alkylation of the active site cysteine of chymopapain by iodoacetate was found to be sufficiently rapid and selective for this reagent to be used as an active-site titrant.

Binding Sites↗
PubMed1990

Immunosuppressive agents in current use.

The use of immunosuppressants has increased as clinical applications for such therapy have become more widespread. Immunosuppressive therapy is now particularly relevant in the field of organ transplantation, a practice that has only developed over the last 20 years. Drugs used as immunosuppressants are discussed in relation to disease category, where they are of value, mode of action, and potential side effects. Future prospects concerning the development and use of immunosuppressants are considered.

Humans↗
PubMed1990

A new look at Pz-peptidase.

Work with new, quenched fluorescence substrates of Pz-peptidase has led to the discovery that Pz-peptidase, soluble metallo-endopeptidase and endo-oligopeptidase A are either identical, or very closely related enzymes. Pz-peptidase is a metallo-endopeptidase with marked thiol-dependence. It has been confirmed that inhibitors of the type designed by Orlowski for soluble metallo-endopeptidase are effective tools in studying Pz-peptidase. There is little evidence to support the proposed role of Pz-peptidase in connective tissue matrix degradation, and the main function of the enzyme may be intracellular.

Amino Acid Sequence↗
PubMed1990

Allogeneic bone marrow transplantation for leukemia in Europe: regional differences. Report from the Leukemia Working party of the European Group for Bone Marrow Transplantation.

The results of 1904 allogeneic HLA identical sibling donor bone marrow transplants performed in 52 European centers between 1979 and 1986 and reported to the EBMT leukemia registry were analysed by geographical location of the transplant. Patients were grouped into six regions: United Kingdom, Nordic Group, Benelux, France, Central Europe and Southern Europe. There were significant differences between these regions with respect to patient population and outcome. The relative proportion of the three major disease categories, stage and subtype of the diseases, graft-versus-host disease prevention methods, donor recipient sex combinations, age of the patient, year of the transplant and the time intervals from diagnosis to transplant, from diagnosis to first complete remission for acute leukemia and the time from first complete remission to the transplant varied from region to region. The analysis of outcome parameters showed a significant difference in relapse incidence from region to region. This influence of region was confirmed in a multivariate analysis and was independent of the other factors known to affect outcome. Leukemia-free survival and transplant-related mortality were not different. The reasons for these differences could not be explained by the data in the registry. We conclude that regional factors must be considered when bone marrow transplant data are compared and we postulate that pretransplant factors probably affect outcome more than was previously realized.

Adolescent↗
PubMed1989

Papaya proteinase IV amino acid sequence.

The amino acid sequence of papaya proteinase IV (PPIV), a major proteinase from the latex of Carica papaya [(1989) Biochem. J. 261, 469-476] is described. The enzyme has a high degree of sequence identity with papaya proteinase III, chymopapain and papain (81, 70 and 67%, respectively), and is clearly a member of the papain superfamily of cysteine proteinases. Nevertheless, the sequence shows substitution of certain residues conserved in all other known members of the superfamily. It is suggested that some of these substitutions may account for the unusual specificity of PPIV.

Amino Acid Sequence↗