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Biomedical subjects

E Harper

Publications and source records attributed to E Harper.

At least 55 records · Page 3Linked to original sources
PubMed1979

Evidence against collagen activation of platelet-associated factor XI as a mechanism for initiating intrinsic clotting.

Collagen activation of platelet-associated Factor XI has been proposed as a mechanism for initiating intrinsic clotting independent of Factor XII. Since this could explain the lack of bleeding in patients with hereditary Factor XII deficiency, prekallikrein deficiency and high molecular weight kininogen deficiency, we subjected the hypothesis to rigorous testing. Incubation of isolated platelets with collagen and calcium ions failed to generate activity shortening the clotting time of an activated Factor XI (XIa) assay that had been modified to eliminate effects due to platelet-associated activated Factor V. Nor could generation of traces of Factor XIa in such mixtures be detected by incubation with purified Factor IX and testing for the generation of activated Factor IX (IXa) in clotting and amidolytic assays. Moreover, when blood or platelet-rich plasma containing added 125I-Factor IX was incubated with calcium ions and collagen and then subjected to reduced sodium dodecyl sulfate polyacrylamide gel electrophoresis, the radioactivity profiles revealed only native 125I-Factor IX without evidence of the polypeptide chains of Factor IXa. The negative results of this study mitigate against the hypothesis that collagen activation of platelet-associated Factor XI represents a physiologically significant mechanism for initiating clotting independent of Factor XII.

Animals↗
PubMed1979

Growth regulators in connective tissues. II. Evidence for the presence of several growth inhibitors in aortic extracts.

Studies on the effects of bovine aorta extracts on endothelial and smooth muscle cells cultured from the same tissue indicate they contain at least four separate molecular species capable of inhibiting cell growth. Two, heparin and a recently characterized dermatan sulfate-chondroitin sulfate proteoglycan, are large polyanions and inhibit the growth of both smooth muscle and endothelial cells, but require large amounts to induce this effect. The other two are low molecular weight molecules which inhibit only the growth of endothelial cells, one of which is a protease inhibitor which has been purified to homogeneity. The fourth and most potent is an as yet unidentified fraction distinguishable from the protease inhibitor. Heparin, as reported by others, and the proteoglycan also enhance collagenase activity. It would therefore appear that aorta contains several molecular species which have the potential to affect both invasive and proliferative processes.

Animals↗
PubMed1978

Platelet factor 4: an inhibitor of collagenase.

Human platelet factor 4 (PF4) is known to bind to heparin and inhibit its anticoagulant effect. This factor also inhibits the enzyme collagenase derived from cultured human skin and collagenase extracted from human granulocytes. The addition of heparin to the PF4-collagenase assay system has no effect on the observed inhibition of collagenase. Thus PF4 inhibits collagenase, in addition to neutralizing heparin.

Blood Coagulation Factors↗
PubMed1978

The specificity of the reaction of collagen with platelets.

1. Human platelets will react with a number of different collagens from guinea-pig to ostrich. 2. Human skin collagen when treated with pepsin does not react with human platelets. 3. Calf platelets display a different pattern of reactivity than that of human platelets.

Animals↗
PubMed1978

Sister chromatid exchanges in lymphocyte cultures of patients receiving chemotherapy for malignant disorders.

The frequency of sister chromatid exchange (SCE) was studied in peripheral lymphocytes of patients receiving chemotherapy for various malignant disorders. Significantly increased SCE frequencies were recorded in six patients 2-7 weeks after CCNU treatment and in one patient 2 weeks after melphalan treatment. One patient treated with prednimustine and one treated with DTIC had SCE frequencies just within the upper limit of the control range 1-2 weeks after therapy. Normal SCE frequencies were recorded in nine patients studied at times varying from 3 days to several weeks after administration of cytostatic courses involving 5-fluorouracil, vincristine, adriamycin, cyclophosphamide, bleomycin, thioTEPA, methotrexate, and prednimustine. Radiotherapy could not be causally related to increased SCE frequencies in any of the patients. The results indicate that CCNU and melphalan, in contrast to several other chemotherapeutic agents, induce very long-lived DNA lesions, which may be of crucial importance for the development of secondary neoplasms.

Adolescent↗
PubMed1977

Tumor cell collagenase and its inhibition by a cartilage-derived protease inhibitor.

Human osteosarcoma and mammary carcinoma cells were cultured separately in a medium supplemented with fetal calf serum, until they were confluent. The medium was then replaced by serum-free medium supplemented with heparin. Both cell cultures secreted collagenase, and this activity was inhibited by a cartilage-derived protein of low molecular weight. Since cartilage is rarely invaded by neoplasms, the presence of this inhibitor may play an important role in the regulation of tumor invasion.

Breast Neoplasms↗
PubMed1976

Collagenase enzymes from Clostridium: characterization of individual enzymes.

Four collagenases have been purified to apparent homogeneity from extracts of Clostridium histolyticum and partially characterized. The four purified enzymes are devoid of hydrolytic activity against casein and the synthetic substrate, benzolyarginine naphthylamide, but all retain activity against native collagen. The enzymes are initially spearated by isoelectric focusing where three of the enzymes show distinct isoelectric points: collagenase I = 5.50, collagenase II = 5.65, and collagenases IIIa and IIIb = 5.90-6.00. Collagenases IIIa and IIIb can be subsequently separated on diethylaminoethylcellulose. The four purified enzymes show single bands upon polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Calibration of the molecular weights on the basis of migration distance shows a marked dependence on gel porosity. At high acrylamide concentration, collagenases I, II, and IIIa appear to converge to a limiting molecular weight congruent to 81 000, while collagenase IIIb has a distinctly lower value congruent to 72 000. The similarity between these molecular weight values and those derived from the sedimentation and diffusion coefficients of the native enzyme indicates that each collagenase is a single polypeptide chain. All of the collagenases have comparable catalytic activities against a series of natural and synthetic substrates and are immunologically cross-reactive. Although all four enzymes are evident upon initial electrofocusing of the crude extract, it is possible that the multiplicity of forms is, at least in part, a consequence of lysis following initial secretion from the cell.

Clostridium↗
PubMed1975

Interchain disulfide bonds in procollagen are located in a large nontriple-helical COOH-terminal domain.

Tadpole collagenase (EC 3.4.24.3) cleaved chick cranial bone procollagen into two triple-stranded fragments, PCA and PCB. Only PCB, with an estimated molecular weight of about 60,000 for each component chain after reduction, was found to contain interchain disulfide bonds. The analogous cleavage of collagen is known to produce a large NH2-terminal fragment with a molecular weight of 70,000 for each chain and a small COOH-terminal fragment containing chains of about 25,000 molecular weight. Since PCB was too small to represent the product NH2-terminal to the site of collagenase cleavage, localization of interchain disulfide bonds to a COOH-terminal domain in procollagen was indicated. This assignment was conformed by Dintzis-type short-term labeling experiments. Procollagen obtained by acid extraction of bone lacked the COOH-terminal disulfide-bonded domain. The findings support a model for procollagen consisting of three proalpha chains each containing nonhelical NH2-terminal extensions of 20,000 molecular weight and COOH-terminal extensions of about 35,000 molecular weight, the latter linked by interchani disulfide bonds.

Animals↗
PubMed1974

Human platelet collagenase.

The presence of proteolytic enzymes such as cathepsin and elastase in platelets and the important role of collagen in platelet aggregation suggested that collagenase might be present in platelets. Epinephrine, ADP, and collagen liberate collagenase from platelets in plasma as measured by the hydrolysis of [(14)C]glycine-labeled collagen fibrils. The collagenase activity appeared in an early phase of platelet aggregation and was not a part of the release reaction. However, only 50% of the total collagenase could be liberated by the aggregating agents used. Sucrose density gradient analysis of platelet homogenates using appropriate sub-cellular markers indicated that collagenase appeared in both the granule and membrane fractions. Gel-filtered platelets failed to show collagenase activity before exposure to aggregating agents but released more collagenolytic activity than was found in platelet-rich plasma. This observation was explained by the finding that collagenolytic activity was inhibited by normal human plasma. One of the inhibitors is alpha(1)-antitrypsin as demonstrated by decreased inhibition in plasma from a patient with homozygous alpha(1)-antitrypsin deficiency. Platelet collagenase activity could also be demonstrated by its ability to decrease the viscosity of collagen solutions and to produce collagen fragments similar to those produced by other mammalian collagenases on disk gel electrophoresis. The observation that partially purified platelet collagenase could destroy the platelet-aggregating activity of collagen suggests that the enzyme might function in a negative feedback mechanism limiting thrombus formation.

Acid Phosphatase↗