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Biomedical subjects

M Silverberg

Publications and source records attributed to M Silverberg.

At least 73 records · Page 4Linked to original sources
PubMed1982

The cleavage and formation of activated human Hageman factor by autodigestion and by kallikrein.

We have compared the cleavage of purified human Hageman factor (HF) by an activated form of human Hageman factor (HFa) (autodigestion) and by kallikrein. In each case, an initial cleavage is seen which produces HFa with Mr = 80,000 consisting of a heavy chain of Mr = 52,000 disulfide-linked to a light chain of Mr = 28,000. As autodigestion proceeds, HFa is shown to be further digested to yield a major active product at a molecular weight of 40,000 as well as Hageman factor fragment (HFf), which appear as two closely related molecular species of Mr = 28,000 and 30,000. A minor active product of Mr = 70,000 is also seen. Upon reduction of each of the active forms, a chain with Mr = 28,000 is released which contains the active site. HF digestion by kallikrein results in rapid formation of HFa, followed by HFa digestion to HFf and degradation of the heavy chain region to an inactive fragment at 40,000 daltons, which is then degraded to an end product of Mr = 36,000. Production of the active species with Mr = 40,000 and 70,000 is greatly diminished when kallikrein is the HF activator, and these active forms are shown to be formed primarily by autodigestion. The time course of HFa and HFf formation indicates that the rate of activation of Hageman factor by kallikrein is much faster than the rate of autoactivation; the addition of high molecular weight kininogen increases the rate of HFa and HFf formation as well as the extent of HG digestion. These data indicate that HFa is the active intermediate from which other active species are derived. The patterns of HF and HFa digestion by HFa and kallikrein are distinct; a model for HF digestion is presented.

Electrophoresis, Polyacrylamide Gel↗
PubMed1982

Progressive esophageal dysfunction in chronic granulomatous disease.

Chronic granulomatous disease of childhood (CGD), a hereditary disorder of neutrophil function, affects the gastrointestinal tract in a variety of ways. Esophageal involvement has only rarely been reported. An 11-year-old boy with CGD and progressive esophageal dysmotility is described. Repeated radiographic, endoscopic, and motility studies revealed a markedly atonic esophagus with varying function of the lower esophageal sphincter. Pharmacologic therapy and esophageal dilatations were unsuccessful in establishing adequate esophageal function. A feeding gastrostomy was required for nutritional support.

Child↗
PubMed1982

Enzymatic activities of activated and zymogen forms of human Hageman factor (factor XII).

Pro-Phe-Arg chloromethylketone (PPACMK) at 5.26 microM inactivated the amidolytic activity of native human Hageman factor with an apparent first-order rate constant of 0.75 min-1. The activated forms of Hageman factor, Hfa and HFf, were also inactivated by PPACMK with rate constants 0.82 and 0.72 min-1. These numbers indicate that the activity detectable in native Hageman factor is due to contamination with activated species. Uncleaved Hageman factor reacts slowly with 40 mM diisopropyl fluorophosphate with concomitant loss of its procoagulant activity. Incubation of native Hageman factor with PPACMK does not destroy its procoagulant activity, even in the presence of the activator dextran sulphate, but PPACMK inhibits autoactivation of Hageman factor, suggesting that no active site is formed in uncleaved, surface-bound Hageman factor. The activation of prekallikrein by Hageman factor under initial-rate conditions occurs after a lag and is prevented by an inhibitor of Hageman factor from corn. The kinetics of prekallikrein activation and the effects of inhibitors provide evidence that the amidolytic and proteolytic activities of human Hageman factor reside in the activated forms derived by limited proteolysis of the native molecule.

Amides↗
PubMed1981

Activation of the classical pathway of complement by Hageman factor fragment.

A fragment of activated Hageman factor (HFf) has been demonstrated to activate the classical pathway of complement in a manner that is analogous to complement activation by antigen-antibody complexes or aggregated IgG. Thus C1, C4, C2, C3, and C5 were found to be depleted on addition of HFf to serum. The reduction of serum hemolytic activity was maximal upon addition of 5 micrograms HFf and an incubation time of 60 min at 37 degrees C. Consumption of the total complement activity and of the individual components proceeded in a dose-dependent fashion. No comparable activity was observed when equimolar concentrations of either the native Hageman factor (HF) or two-chain activated form of Hageman factor (HFa) were incubated with serum. Further, the ability of HFf to convert serum C3 and C4 was similar to that of aggregated IgG as assessed by immunoelectrophoresis. This function of HFf appeared to be independent of plasminogen (or plasmin) since plasminogen-free serum was indistinguishable from normal serum. Radial double immunodiffusion experiments using antiserum to C1q, C1r, and C1s on HFf-treated serum demonstrated the dissociation of the C1 trimolecular complex, with concomitant reduction of C1r antigenicity that is indicative of C1 activation. Thus, HFf appears to lead to C1 activation upon incubation with serum or when incubated with partially purified C1. This may represent a control link between activation of the intrinsic coagulation-kinin pathway and the initiation of the classical complement cascade.

Animals↗
PubMed1981

Mechanisms for Hageman factor activation and role of HMW kininogen as a coagulation cofactor.

Our present concept of the initiating reactions of the intrinsic coagulation pathway is outlined in Figure 5. Although we remain unsure of the etiology shown in Figures 3 and 4, the major function of HMW kininogen is to bind prekallikrein and factor XI in plasma and attach them to surfaces in a conformation that allows activation by HFa. The HMW kininogen--dependent augmentation of the binding of prekallikrein and factor XI to the surface that is seen in plasma (but not buffer systems) would appear to be of lesser importance. Once activated, however, dissociation of kallikrein from the surface allows it to attack adjacent Hageman factor molecules on the same or other particles; this reaction appears to be more rapid than the rate of Hageman factor autoactivation. Thus, the rapid burst of HFa formation seen in normal plasma is kallikrein dependent. It is also dependent upon HMW kininogen, but this appears to be an indirect relationship. The HMW kininogen augments the amount of prekallikrein bound, allows activation to kallikrein, and is needed for kallikrein dissociation from the surface. These three effects all yield a marked increase in the effective ratio of kallikrein/Hageman factor at the surface-fluid interface, and this may be the condition required for rapid HFa formation.

Binding Sites↗
PubMed1981

The intrinsic coagulation-kinin pathway, complement cascades, plasma renin-angiotensin system, and their interrelationships.

Activation of the classical complement pathway is initiated by immune complexes consisting of IgM antibody or IgG subclasses 1, 2, and 3. Binding to Clq leads to activation of C1s and digestion of C4 and C2 to yield a C3 convertase. The alternative complement pathway is initiated by complex polysaccharides as well as immune complexes of the IgA class which interact with Factors B, D, C3, and properdin to yield a stabilized C3 convertase consisting of PC3Bb. Cleavage of C3 and C5 by either pathway yields the C3a and C5a anaphylatoxins which cause histamine release from mast cells and formation of the C5b6789 attack complex causes cell lysis. Both immunologic and nonimmunologic tissue damage can initiate the surface dependent pathways of coagulation, fibrinolysis, and kinin formation. Surface bound Hageman Factor interacts with complexes of prekallikrein and HMW-kininogen as well as Factor XI and HMW-kininogen to form activated Hageman factor, kallikrein, and Factor XIa. Factor XIa continues the coagulation pathway, kallikrein and Factor XIa convert plasminogen to plasmin and kallikrein digests HMW-kininogen to yield bradykinin. The Cl inhibitor, which inactivates Cls is the major plasma inhibitor of activated Hageman factor and kallikrein. In its absence, a potentially fatal form of angioedema is seen. The inactivator of the C3a and C5a anaphylatoxins is identical to carboxypeptidase N, the major plasma inactivator of bradykinin thus demonstrating the common control mechanisms which regulate the complement and kinin-forming pathways.

Blood Coagulation↗
PubMed1980

Autoactivation of human Hageman factor. Demonstration utilizing a synthetic substrate.

The kallikrein substrate H-D-Pro-Phe-Arg-p-nitroanilide was used in a direct spectrophotometric assay for activated Hageman factor (HF). An 80,000-dalton two-chain, disulfide-linked enzyme, termed HFa, and a 28,000-dalton Hageman factor cleavage product, HFf, were not distinguished in this assay and had a Km of 190 microM and kcat of 15/s. Treatment of HF with 10(-2) M diisopropylfluorophosphate yielded preparations containing 0.2 to 0.9% activated HF as assessed in plastic cuvettes. In quartz cuvettes, concave upward progress curves were obtained. Secondary plots of absorbance/time against time were also nonlinear and consistent with an increased rate of formation of activated enzyme. The curves varied with total protein content and synthetic substrate concentration in a manner consistent with autoactivation; increasing synthetic substrate competed with native HF for interaction with activated HF. Accelerated cleavage of surface-bound radiolabeled HF was demonstrated after incubation with HFa but not HFf, indicating that HFa is the form of active enzyme responsible for autocleavage. The autoactivation described herein may provide a sufficient initial concentration of activated HF to initiate the intrinsic coagulation, fibrinolytic, and kinin-forming cascade.

Anilides↗
PubMed1980

Zinc status and its relation to growth retardation in children with chronic inflammatory bowel disease.

Zinc status was studied in 30 patients with chronic inflammatory bowel disease (CIBD) as well as in 17 normal children, 13 primordial short stature, and 17 anorexia nervosa patients. Basal serum and urinary excretion levels of zinc were measured in all patients. In addition, a zinc loading test was performed in 16 CIBD patients, 21 normal and/or short stature children, and nine patients with anorexia nervosa. Eleven of 30 patients with CIBD had serum zinc values less than 0.7 microgram/ml, whereas none of the other patients had hypozincemia. In addition, the mean urinary zinc excretion of CIBD patients was significantly lower than that of patients with primordial short stature and with anorexia nervosa. An altered response to oral zinc load was the most frequent abnormality in CIBD patients. Those with moderate and severe clinical disease activity had a decreased serum rise of zinc after the oral load of this ion. Urinary excretion of zinc after oral load was also marked by deficiency in all CIBD patients. The abnormalities of zinc metabolism were more frequent among the CIBD patients with growth abnormalities, although they were also found in patients who had normal growth. Among the 14 patients with CIBD and growth abnormalities, seven were hypozincemic and four hypozincuric. Hypozincemia was only found in four patients who had normal height; however, the growth velocity was not known. The zinc tolerance test revealed abnormalities in four of five CIBD patients with short stature and in two of three patients with slow growth. On the other hand, similar alterations in zinc tolerance tests were seen in three of seven CIBD patients with normal height and growth.

Adolescent↗
PubMed1979

Plasmin can activate plasma prorenin but is not required for the alkaline phase of acid activation.

1. Plasma prorenin is an inactive form of renin that is converted into active renin at alkaline pH in previously acidified plasma; this conversion of prorenin into renin is mediated by Hageman factor-dependent activation of prekallikrein, which, in turn, leads to prorenin activation. 2. Since plasma kallikrein can activate plasminogen, the present studies were designed to evaluate whether alkaline-phase activation of prorenin by plasma kallikrein is mediated via plasminogen activation. 3. We demonstrated that plaminogen is present in acid-treated plasma in sufficient quantity to convert prorenin into renin after activation by streptokinase. 4. However, alkaline-phase activation was completely normal in plasminogen-free plasma. 5. Therefore alkaline-phase activation of plasma prorenin is mediated by plasma kallikrein but is not dependent on kallikrein activation of plasminogen.

Enzyme Activation↗
PubMed1979

Initiation of plasma prorenin activation by Hageman factor-dependent conversion of plasma prekallikrein to kallikrein.

Plasma prorenin is an inactive form of renin (EC 3.4.99.19) that can be converted to active renin in acid-treated plasma by an endogenous serine protease that is active at alkaline pH (alkaline phase activation). To identify this enzyme we first tested the ability of Hageman factor fragments, plasma kallikrein (EC 3.4.21.8), and plasmin (EC 3.4.21.7) to activate prorenin in acid-treated plasma. All three enzymes initiated prorenin activation; 50% activation was achieved with Hageman factor fragments at 1 microgram/ml, plasma kallikrein at 2-4 microgram/ml, or plasmin at 5-10 microgram/ml. We then showed that the alkaline phase of acid activation occurred normally in plasminogen-free plasma but was almost completely absent in plasmas deficient in either Hageman factor or prekallikrein; alkaline phase activation was restored to these latter plasmas when equal parts were mixed together. Therefore, both Hageman factor and prekallikrein were required for alkaline phase activation to occur. We then found that, although plasma kallikrein could activate prorenin in plasma deficient in either Hageman factor or prekallikrein, Hageman factor fragments were unable to activate prorenin in prekallikrein-deficient plasma. These studies demonstrate that alkaline phase prorenin activation is initiated by Hageman factor-dependent conversion of prekallikrein to kallikrein which, in turn, leads to activation of prorenin. In this fashion, we have revealed a possible link between the coagulation-kinin pathway and the renin-angiotensin system.

Angiotensin I↗