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H Kaplan

Publications and source records attributed to H Kaplan.

At least 19 recordsLinked to original sources
PubMed1992

Similarities in melittin functional group reactivities during self-association and association with lipid bilayers.

Competitive labeling of melittin over a range of concentrations in the presence and absence of liposomes provides a series of "snapshots" of the chemical reactivities of melittin's intrinsic nucleophiles. Distinct trends in apparent reactivities were observed for the Gly-1 alpha-amino group and the epsilon-amino groups of Lys-7 and Lys-21 and -23, over a range of concentrations, providing evidence for different forms of associated melittin in solution. The monomer-tetramer transition can be followed, in accord with structural details derived from X-ray crystallography. The reactivity behavior of the alpha-amino group of Gly-1 and the epsilon-amino groups of Lys-21 and Lys-23 suggests these groups undergo similar perturbations in their microenvironments during the monomer-tetramer transition in free solution. Similar changes in reactivity behavior occur upon association of melittin monomers with bilayer-forming lipids. Together, these findings suggest that the local environments of the N- and C-terminal segments have similar physicochemical properties in both the solution tetramer and the lipid-associated complex. The concentration dependence of the chemical properties of melittin is correlated with surface accessibility calculations which are used to provide a framework for interpretation. Aspects of several previously proposed models of membrane lysis can be accounted for by concentration-dependent properties of melittin.

Amino Acid Sequence↗
PubMed1992

Bacillus thuringiensis crystal protein: effect of chemical modification of the cysteine and lysine residues.

The 16 cysteine residues of reduced protoxin from Bacillus thuringiensis subsp. kurstaki HD-73 can be quantitatively reacted with: (a) iodoacetic acid, to give carboxymethyl protoxin; (b) iodoacetamide, giving carbaminomethyl protoxin and (c) N-(beta-iodoethyl)trifluoroacetamide to give aminoethyl protoxin. The carboxymethyl derivative was found to be significantly more soluble at neutral pH values where both the native protoxin and the carbaminomethyl derivative exhibit low solubilities. At the alkaline pH values (pH 9.5-10.5) normally used to solubilize the crystal protein, the native protein was slightly more soluble than either the carboxymethyl or the carbaminomethyl derivatives. The aminoethyl derivative had an extremely low solubility at all pH values. Succinic anhydride reacted with only 35% of the lysine residues in both the carboxymethyl and the carbaminomethyl protoxin derivatives. Nonetheless, these succinylated protoxins exhibited significantly increased solubilities at neutral pH values. All the derivatives were found to retain full insecticidal activity toward spruce budworm (Choristeneura fufimerana) larvae. It is concluded that all the cysteine residues and modified lysine residues are on the surface of the protein and that derivatization does not alter the conformation of the solubilized protoxin.

Bacillus thuringiensis↗
PubMed1991

The toxic moiety of the Bacillus thuringiensis protoxin undergoes a conformational change upon activation.

Proteolytic processing of the 133-kDa crystal protein (protoxin) from Bacillus thuringiensis subsp. kurstaki yields a 67-kDa insecticidal toxin. Differential scanning calorimetry was used to investigate whether the toxic moiety in the protoxin molecule has the same conformation as activated toxin. Compared to protoxin, toxin gives rise to a more complex endotherm which extends over a 10 degrees C broader temperature range and contains a component occurring at a substantially higher temperature than any unfolding transition in the protoxin endotherm. It is concluded that the toxic moiety undergoes a conformational change upon activation in which the thermal stability of at least one of its domains is significantly increased.

Bacillus thuringiensis↗
PubMed1991

The mechanism of sunlight-mediated inactivation of Bacillus thuringiensis crystals.

Detailed photostability studies were carried out using purified delta-endotoxin crystals from Bacillus thuringiensis subspecies HD-1 and HD-73. The mechanism and time course of sunlight inactivation was investigated by: (a) monitoring the tryptophan damage in the intact crystals by Raman spectroscopy, (b) amino acid analysis and (c) biological assays using insects. The results demonstrate that, for purified HD-1 or HD-73 crystals, the 300-380 nm range of the solar spectrum is largely responsible for bringing about crystal damage and consequent loss of toxicity. Purified Bacillus thuringiensis crystals that were exposed to fermentation liquor after cell lysis were more quickly degraded by sunlight than were crystals from cells that were lysed in water. This effect is attributed to adsorption of chromophores by crystals exposed to the fermenter liquor and the subsequent ability of these chromophores to act as photosensitizers. The importance of a photosensitization mechanism in crystal degradation was further emphasized by irradiating Bacillus thuringiensis crystals in vacuo. The latter crystals were found to be less damaged (20% tryptophan loss after 24 h irradiation by the solar spectrum) compared with crystals from the same sample irradiated in air (60% (60% tryptophan loss). Other methods of decreasing exposure of the crystals to oxygen, e.g. by using glycerol as a humectant, were also found to be successful in controlling photodamage. The results concerning photodegradation support a photosensitization mechanism involving the presence of exogenous (and possibly endogenous) chromophores which create singlet oxygen species upon irradiation by light.

Amino Acids↗
PubMed1991

A non-cytotoxic suppressor of immunoglobulin synthesis and secretion by B cells of normal humans and patients with rheumatoid arthritis and systemic lupus erythematosus.

A factor secreted by thymocytes of immunized rabbits totally suppressed both the initiation of, and ongoing synthesis and secretion of, lectin (PWM)-induced synthesis of IgM and IgG immunoglobulins by the circulating B lymphocytes of normal humans, and of twenty consecutive patients with rheumatoid arthritis and twelve consecutive patients with systemic lupus erythematosus. The suppressor factor, referred to as human Ig synthesis/secretion suppressor factor or HISSF, is not HLA restricted in its activity and is not cytotoxic to the circulating human mononuclear cells (B cells, T cells, Null cells and monocytes). It was demonstrated that T cells precultured with HISSF were transformed into suppressor cells which, when added to fresh cultures of autologous B cells, suppressed the synthesis and secretion of IgM and IgG. On the basis of its suppressive and non-cytotoxic properties in vitro, HISSF may be an effective immunosuppressant in the treatment of patients with autoimmune diseases.

Animals↗
PubMed1991

Communication Self-Assessment Scale Inventory for Deaf Adults.

The Communication Self-Assessment Scale for Deaf Adults (CSDA) evaluates difficult communication situations, their importance to the respondent, communication strategies, and communication attitudes. Scale items use simple descriptive language in active declarative form. Each scale is comprised of three or more subscales. The subject responds using a three point semantic differential based on frequency of occurrence or degree of importance. Item analysis, factor analysis, internal consistency reliability studies, and collection of normative data have been performed on a population of 290 deaf adults.

Adult↗
PubMed1991

Repair of the severely contracted socket with meshed skin graft and semi-rigid conformer.

Nine severely contracted sockets were reconstructed using a meshed skin graft in conjunction with a semi-rigid conformer-stent. Particularly useful following unsuccessful surgery with mucosal grafting, or in cases where for some reason mucosal grafts cannot be obtained, this technique is superior to current procedures utilizing nonmeshed split-thickness skin grafts.

Adolescent↗
PubMed1991

Methotrexate in rheumatoid arthritis: effects on disease activity in a multicenter prospective study.

One hundred and twenty-three patients with rheumatoid arthritis (RA) who successfully completed a randomized trial comparing oral methotrexate (MTX) to auranofin enrolled in a longterm prospective study of oral MTX. Of the 91 patients who completed 24 months of therapy, a significant (p = 0.0001) improvement was noted compared to baseline in all clinical disease variables and the Westergren erythrocyte sedimentation rate (ESR). Marked improvement occurred in 94 (76%) and 98 (80%) of the patients in the joint pain/tenderness index and joint swelling index at the last evaluable visit (mean 26 months). Of the 77 patients with an elevated ESR at baseline, 29 (38%) patients normalized it (less than 20 mm/h) while receiving therapy (p less than 0.01). A significant reduction in prednisone dose was also seen. Adverse events occurred frequently but were generally mild in severity. Twenty-seven patients (22%) withdrew during the study. Four (3%) withdrew due to lack of efficacy, and 6 (5%) because of adverse experiences. The overall probability of continuing therapy in the study for 48 months was projected at 72%. This large prospective study supports the observation of earlier smaller studies that MTX is an effective drug in the treatment of RA.

Administration, Oral↗
PubMed1991

Hyperalgesia during acute opioid abstinence: evidence for a nociceptive facilitating function of the rostral ventromedial medulla.

Naloxone-precipitated opioid abstinence is associated with enhancement of reflex responses to noxious stimulation (hyperalgesia). The present experiments in lightly anesthetized rats were designed to determine (1) whether neurons in the rostral ventromedial medulla (RVM) contribute to this enhancement, and (2) whether this enhancement is due to removal of an inhibitory modulatory influence or to activation of a facilitatory influence. In the first experiment, 10 micrograms of morphine was microinjected into the RVM; subsequent administration of naloxone (1 mg/kg, i.v.) shortened tail-flick latency. This is evidence that a synaptic action of opioids within the RVM can contribute to hyperalgesia. In the second experiment, systemic administration of morphine (2 mg/kg, i.v.) was followed by systemic administration of naloxone (1 mg/kg, i.v.), which produced a significant hyperalgesia that could be markedly attenuated by microinjection of 10 micrograms lidocaine into the RVM. That inactivation of RVM reduces the hyperalgesia indicates that the CNS is capable of generating a facilitating action on nociceptive transmission. Previous studies from this laboratory have indicated that a population of RVM neurons, on-cells, shows increased activity during opioid abstinence. The present experiments support the hypothesis that RVM on-cells exert a facilitating influence on nociceptive transmission.

Animals↗
PubMed1990

Folding and unfolding of the protoxin from Bacillus thuringiensis: evidence that the toxic moiety is present in an active conformation.

The action of trypsin or papain on the 130-kDa crystal protein (protoxin) from Bacillus thuringiensis subsp. kurstaki HD-73 yields a 67-kDa proteinase-resistant toxic fragment (toxin) which is derived from the N-terminal half of the molecule. Sensitivity to proteolysis and fluorescence emission spectroscopy showed that the toxin unfolded to a much greater extent in 6 M guanidinium chloride (GuHCl) than in 8 M urea. Protoxin also unfolded extensively in 6 M GuHCl, whereas in 8 M urea only the C-terminal half of the molecule had unfolded extensively. Both unfolded protoxin and unfolded toxin refolded to their native and biologically active conformations. The biphasic unfolding observed for protoxin suggests that the C-terminal half of the molecule unfolded rapidly, whereas the N-terminal toxic moiety unfolded at a much slower rate, similar to that of the free 67-kDa toxin. A 67-kDa fragment, derived from the N-terminal half of the molecule, could be generated from the protoxin in the presence of either urea or GuHCl by treatment with proteinases. Compared to toxin in denaturants, this fragment was found to be more sensitive to proteolysis. However, on removal of the denaturants the fragment had the same proteinase resistance and cytolytic activity as native toxin. The increased proteinase sensitivity of the fragment generated in the presence of denaturants appears to be due to a perturbation in the conformation of the N-terminal toxic moiety. This perturbation is attributed to the unfolding of the C-terminal region of the protoxin prior to its proteolysis to yield the 67-kDa fragment.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacillus thuringiensis↗
PubMed1990

[One-stage flap reconstruction of mandibular defects].

Reconstruction of mandibular defects following severe trauma or resection for malignancy presents a challenge. The mandibular shape and the close relationship of the bone to intra- and extra-oral soft tissues, make surgical procedures difficult. Reconstruction has to correct the bony and soft tissue defects, preserve mandibular functions (mastication, speech and swallowing), and allow the patient to wear dentures and to present an esthetic appearance. Techniques used for mandibular reconstruction have included implants of synthetic materials or rebuilding with autogenous bone grafts, and require a well-vascularized recipient bed. We used the free osteocutaneous scapular and iliac flap techniques, which avoid the disadvantages of local flaps and grafts. They were used in 3 patients after mandibular resection for fibrous dysplasia, osteosarcoma, and squamous cell carcinoma of the oral mucosa invading the mandible, respectively.

Adult↗
PubMed1990

Unusual proteolysis of the protoxin and toxin from Bacillus thuringiensis. Structural implications.

Trypsin is shown to generate an insecticidal toxin from the 130-kDa protoxin of Bacillus thuringiensis subsp. kurstaki HD-73 by an unusual proteolytic process. Seven specific cleavages are shown to occur in an ordered sequence starting at the C-terminus of the protoxin and proceeding toward the N-terminal region. At each step, C-terminal fragments of approximately 10 kDa are produced and rapidly proteolyzed to small peptides. The sequential proteolysis ends with a 67-kDa toxin which is resistant to further proteolysis. However, the toxin could be specifically split into two fragments by proteinases as it unfolded under denaturing conditions. Papain cleaved the toxin at glycine 327 to give a 34.5-kDa N-terminal fragment and a 32.3-kDa C-terminal fragment. Similar fragments could be generated by elastase and trypsin. The N-terminal fragment corresponds to the conserved N-terminal domain predicted from the gene-deduced sequence analysis of toxins from various subspecies of B. thuringiensis, and the C-terminal fragment is the predicted hypervariable sequence domain. A double-peaked transition was observed for the toxin by differential scanning calorimetry, consistent with two or more independent folding domains. It is concluded that the N- and C-terminal regions of the protoxin are two multidomain regions which give unique structural and biological properties to the molecule.

Amino Acid Sequence↗
PubMed1990

Characterization of the cysteine residues and disulphide linkages in the protein crystal of Bacillus thuringiensis.

Bacillus thuringiensis produces a 130-140 kDa insecticidal protein in the form of a bipyramidal crystal. The protein in the crystals from the subspecies kurstaki HD-1 and entomocidus was found to contain 16-18 cysteine residues per molecule, present primarily in the disulphide form as cystine. Evidence that all the cysteine residues form symmetrical interchain disulphide linkages in the protein crystal was obtained from the following results: (i) the disulphide diagonal procedure [Brown & Hartley (1966) Biochem. J. 101, 214-228] gave only unpaired cysteic acid peptides in diagonal maps; (ii) the disulphide bridges were shown to be labile in dilute alkali and the crystal protein could be released quantitatively with 1 mM-2-mercaptoethanol; (iii) the thiol groups of the released crystal protein were shown by competitive labelling [Kaplan, Stevenson & Hartley (1971) Biochem. J. 124, 289-299] to have the same chemical properties as exposed groups on the surface of the protein; (iv) the thiol groups in the released crystal protein reacted quantitatively with iodoacetate or iodoacetamide. The finding that all the disulphide linkages in the protein crystal are interchain and symmetrical accounts for its alkali-lability and for the high degree of conservation in the primary structure of the cystine-containing regions of the protein from various subspecies.

Amino Acids↗
PubMed1990

Low-dose methotrexate compared with auranofin in adult rheumatoid arthritis. A thirty-six-week, double-blind trial.

Weekly treatment with low-dose oral methotrexate (MTX) was compared with daily auranofin (AUR) treatment in a 36-week double-blind, randomized, multicenter study of 281 patients with active, adult-onset rheumatoid arthritis. Both treatment groups showed significant improvement by the usual measures of clinical efficacy. The response with MTX occurred earlier and was consistently greater than that with AUR. An intent-to-treat analysis showed significantly greater improvement (P less than 0.01) with MTX for painful and swollen joint counts and physician and patient global assessments of disease activity. Adverse reactions were reported more frequently in the AUR group, and more AUR-treated patients were withdrawn from the study because of toxicity. MTX was thus more effective and better tolerated than AUR in this study.

Administration, Oral↗
PubMed1990

Secondary structure of the entomocidal toxin from Bacillus thuringiensis subsp. kurstaki HD-73.

The secondary structure of the toxin from Bacillus thuringiensis subsp. kurstaki (Btk) HD-73 was estimated by Raman, infrared, and circular dichroism spectroscopy, and by predictive methods. Circular dichroism and infrared spectroscopy gave an estimate of 33-40% alpha-helix, whereas Raman and predictive methods gave approximately 20%. Raman and circular dichroism spectra, as well as predictive methods, indicated that the toxin contains 32-40% beta-sheet structure, whereas infrared spectroscopy gave a slightly lower estimate. Thus, all of these approaches are in agreement that the native conformation of Btk HD-73 toxin is highly folded and contains considerable amounts of both alpha-helical and beta-sheet structures. No significant differences were detected in the secondary structure of the toxin either in solution or as a hydrated pellet.

Bacillus thuringiensis↗