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M Rosenblatt

Publications and source records attributed to M Rosenblatt.

At least 127 records · Page 7Linked to original sources
PubMed1987

Solid-phase synthesis of melittin: purification and functional characterization.

The main component of the honey bee venom, melittin, is a cationic polypeptide containing 26 amino acids. Exposure of lipid bilayers to this peptide results in the formation of anion-selective channels with a variety of unit conductances. One of the possible causes for this heterogeneity in the conductance could be heterogeneity of the melittin preparation, and indeed, the existence of two prominent forms of naturally occurring melittin, differing only at the N-terminal amino group, has been documented. This paper describes the synthesis of the major form of melittin, using stepwise solid-phase methodology and the demonstration that the synthetic melittin, devoid of the minor component (N-formylmelittin) and other contaminants, interacts with lipid bilayers to form channels which are qualitatively indistinguishable from the ones formed by the naturally occurring toxin. This result indicates that the heterogeneity in the channels produced in bilayers by bee venom is not due to differences in the channel-forming properties of the formyl and non-formyl melittin but rather to differences in the number and orientation of melittin monomers of identical primary structure as they aggregate to form channels in the lipid bilayer.

Bee Venoms↗
PubMed1987

Synthetic signal peptide and analogs display different activities in mammalian and plant in vitro secretion systems.

The biological properties of four chemically synthesized signal peptides were compared in mammalian (rabbit reticulocyte) and plant (wheat germ) cell-free protein secretion systems. The precursor-specific region of bovine pre-proparathyroid hormone (preproPTH), [D-Tyr-(+1)]preproPTH-(-29-+1)amide, and a sulfur-free analog, [Nle-(-25), Nle-(-21), Nle-(-18), Ala-(-14), D-Tyr-(+1)]preproPTH-(-29-+1)amide, inhibit the processing of an unrelated precursor protein (pre-prolactin) to its mature secreted form (prolactin) in the mammalian system. In the plant system supplemented with signal recognition particle, the signal peptides arrest translation of both secretory (preprolactin) and cytoplasmic (globin) proteins. One analog, [Nle-(-25), Nle-(-21), Asp-(-18), Ala-(-14), D-Tyr-(+1)]preproPTH-(-29-+1)amide, inhibits preprotein processing in the mammalian system but fails to induce translation arrest in the plant system. A truncated peptide, [N alpha-AcLeu-(-17), Ala-(-14), D-Tyr-(+1)]preproPTH-(-17-+1)amide, lacking the N-terminal (positively charged) region and a portion of the hydrophobic core region, is inactive in both systems. These studies demonstrate that the chemically synthesized signal region of a precursor protein interacts directly with signal recognition particle and functionally mimics the proposed properties of a native signal sequence linked to a nascent protein as it emerges from the ribosome during biosynthesis, and an analog of the signal peptide reveals fundamental differences between the components involved in the protein secretion apparatus in mammals and plants.

Amino Acid Sequence↗
PubMed1987

Endogenous opioids and ventilatory adaptation to prolonged hypoxia in goats.

To investigate whether endogenous opioid peptides mediate time-dependent changes in ventilatory control during prolonged hypoxia, we studied four adult goats at rest during 14 days at simulated high altitude in a hypobaric chamber (PB approximately 450 Torr). Arterial PCO2 fell during the first several hours of hypoxia, remained stable over the next 7 days, and then rose slightly (but without statistical significance) by day 14. Ventilatory responsiveness to CO2 increased during the first week of hypoxia. By day 14, while still greater than control, the ventilatory response to CO2 was less than that observed on day 7. Immunoactive beta-endorphin levels in plasma and CSF did not change during the 14-day period. Administration of naloxone on day 14 did not restore the ventilatory response to CO2 to the level observed during the first week of acclimatization. We conclude that in adult goats, time-dependent changes in ventilatory response to CO2 during acclimatization to prolonged hypoxia are not primarily attributable to alterations in endogenous opioid peptide activity.

Adaptation, Physiological↗
PubMed1987

Immunoprecipitation of the parathyroid hormone receptor.

An 125I-labeled synthetic analog of bovine parathyroid hormone, [8-norleucine,18-norleucine,34-tyrosine]PTH-(1-34) amide ([Nle]PTH-(1-34)-NH2), purified by high-pressure liquid chromatography (HPLC), was employed to label the parathyroid hormone (PTH) receptor in cell lines derived from PTH target tissues: the ROS 17/2.8 rat osteosarcoma of bone and the CV1 and COS monkey kidney lines. After incubation of the radioligand with intact cultured cells, the hormone was covalently attached to receptors by using either a photoaffinity technique or chemical (affinity) cross-linking. In each case, covalent labeling was specific, as evidenced by a reduction of labeling when excess competing nonradioactive ligand was present. After covalent attachment of radioligand, membranes were prepared from the cells and solubilized in the nonionic detergent Nonidet P-40 or octyl glucoside. The soluble membrane fraction present in the supernatant of a 100,000 X g centrifugation was incubated with IgG prepared from anti-PTH antiserum generated to the amino-terminal region, residues 1-34, of PTH. The IgG-PTH-receptor complex was precipitated with staphylococcal protein A-Sepharose. Analysis of the immunoprecipitate on NaDod-SO4/polyacrylamide gel electrophoresis followed by autoradiography revealed the presence of a doublet of apparent molecular mass 69-70 kDa. Specifically labeled bands of approximate molecular mass 95 and 28 kDa were also observed. The anti-PTH IgG was affinity purified by passage over a PTH-Sepharose column and used to make an immunoaffinity column. The 70- and 28-kDa bands were also observed after labeled solubilized membrane preparations were allowed to bind to this column and then were eluted by using a [Nle]PTH-(1-34)-NH2-containing buffer or acetic acid. These studies suggest that the use of an anti-PTH antiserum that binds receptor-bound hormone is likely to be a useful step in the further physiochemical characterization and purification of the PTH receptor.

Animals↗
PubMed1987

Evaluation of a parathyroid hormone antagonist in an in vivo multiparameter bioassay.

The antagonist properties of a bovine parathyroid hormone analogue ([Tyr34]bPTH-(7-34] amide were quantitatively assessed in vivo in a multiparameter assay to estimate the potency of the antagonist against the major actions of PTH. The analogue inhibited PTH-stimulated urinary excretion of phosphate and adenosine 3',5'-cyclic monophosphate in vitamin D-deficient thyroparathyroidectomized rats in a dose-dependent manner. At a molar dose ratio as low as 5:1 of antagonist to PTH, partial inhibition occurred. PTH stimulates the activity of 25-hydroxyvitamin D3-1 alpha-hydroxylase in renal proximal tubules. When coinfused with PTH, this analogue completely inhibited PTH-stimulated 1 alpha-hydroxylase activity at a molar dose ratio of 25:1 of antagonist to PTH and partially inhibited the activity at a molar dose ratio of 10:1. The analogue revealed no PTH-like agonist activity for stimulation of the 1 alpha-hydroxylase. Taken together, these studies indicate that [Tyr34]bPTH-(7-34) amide is a potent antagonist of several of the parameters of PTH action in vivo and demonstrate the feasibility of designing a PTH antagonist that can interact simultaneously with all the PTH receptors responsible for the hormone's major actions in vivo.

Animals↗
PubMed1987

Parathyroid hormonelike protein from human renal carcinoma cells. Structural and functional homology with parathyroid hormone.

A variety of solid tumors secrete proteins that are immunochemically distinct from parathyroid hormone (PTH) but activate PTH-responsive adenylate cyclase. Such PTH-like proteins have been proposed as mediators of the hypercalcemia and hypophosphatemia frequently associated with malignancies. We purified to apparent homogeneity a PTH-like protein with a molecular weight of 6,000, that is produced by human renal carcinoma cells. The amino-terminal sequence of the PTH-like protein and that of human PTH were found to display at least five identities in the first 13 positions. The purified protein bound to PTH receptors, activated adenylate cyclase in renal plasma membranes, and stimulated cAMP formation in rat osteosarcoma cells. The PTH-like protein reproduced two additional effects of PTH, stimulation of bone resorption in fetal rat limb bone cultures and inhibition of phosphate uptake in cultured opossum kidney cells. These properties are consistent with a role for PTH-like proteins as mediators of the syndrome of malignancy-associated hypercalcemia.

Carcinoma, Renal Cell↗
PubMed1987

Atrial natriuretic factor receptors.

All of the actions of atrial natriuretic factor (ANF) can be explained on the basis of ANF's interaction with specific receptors on the plasma membrane of cells in target tissues. These receptors have been identified. Binding to these receptors by ANF is time dependent and specific and occurs with high affinity. Numerous analogues of ANF have been synthesized, and in general, their affinity for ANF receptors corresponds closely to their potency in vitro and in vivo. Considerable progress has been made in physicochemically characterizing ANF receptors by photoaffinity labeling and affinity cross-linking techniques.

Animals↗
PubMed1986

Demonstration of post-translational secretion of human placental lactogen by a mammalian in vitro translation system.

This study demonstrates the post-translational translocation across the rough endoplasmic reticular membrane of a mammalian secretory protein, human preplacental lactogen. In the rabbit reticulocyte lysate, human preplacental lactogen biosynthesis is arrested by addition of cycloheximide prior to supplementation with dog pancreatic microsomal membranes, which have previously been shown to translocate and process nascent secretory proteins in a cotranslational manner. Twenty-five percent of the precursor protein is consistently converted to its mature form under these post-translational conditions. The resulting mature hormone is resistant to proteolytic degradation by added proteases, thus indicating that it is translocated across the microsomal membrane and sequestered within the lumenal space of the microsomal vesicles. Approximately one-half of the precursor protein synthesized is associated with the ribosomes. Only the ribosome-associated fraction is secreted in this in vitro system, suggesting that the process of post-translational secretion requires ribosomes for protein interaction with the elements of a subcellular secretory apparatus.

Animals↗
PubMed1986

Response to low-dose pulsatile cortisol in Addison's disease with suspected corticotropinoma.

A 65 year old woman with long-standing Addison's disease treated with oral glucocorticoid and mineralocorticoid replacement had persistently high ACTH levels, inadequate suppression of ACTH on low-dose dexamethasone, sellar enlargement, and pigmentation, and thus resembled patients alleged to develop corticotropinomas while on oral replacement for adrenal insufficiency. Since animal studies suggested that rapid rises of corticosteroids within the physiologic range can inhibit ACTH release, we administered brief infusions of cortisol every three hours with total daily dose equal to her chronic dose. Prompt suppression of ACTH and immunoreactive beta-endorphin occurred during each cortisol dose profiled, suggesting a role for ultradian cortisol fluctuations in tonic inhibition of ACTH secretion in humans, and a possible therapeutic benefit of mimicking ultradian cortisol rhythms during replacement therapy.

Addison Disease↗
PubMed1986

Inhibition of the in vivo parathyroid hormone-mediated calcemic response in rats by a synthetic hormone antagonist.

The parathyroid hormone (PTH) analog, [Tyr34]bovine PTH-(7-34)-amide, can inhibit the PTH-mediated elevation of plasma calcium in thyroparathyroidectomized rats in vivo. The analog is devoid of PTH-like agonist activity in this system. Repeated doses of analog inhibit the animal's calcemic response to PTH. The elevation in serum calcium levels mediated by PTH in this assay reflects PTH action (calcium mobilization) on bone. Earlier studies demonstrated antagonist properties of the analog in a renal-based assay; PTH-stimulated increases in urinary phosphate and cyclic AMP excretion were completely inhibited by the synthetic analog. Along with previous studies, this report indicates that [Tyr34]bovine PTH-(7-34)-amide is an effective in vivo antagonist for several major parameters of PTH action in both kidney and bone.

Animals↗
PubMed1986

Deconvolution of non-Gaussian linear processes with vanishing spectral values.

We consider the problem of estimating the filter generating a non-Gaussian linear process and the deconvolution of that process when the spectral density of the process has zeros. Without using a minimum phase assumption we show that often if there are only finitely many zeros there are procedures to effect such an estimation and deconvolution.

Journal Article↗
PubMed1986

Development and application of a mid-region specific assay for human parathyroid hormone.

A new peptide spanning residues 28-54 of human parathyroid hormone (PTH) was synthesized and used to develop a homologous immunoradiometric assay specific for the mid-region of human PTH. The peptide was coupled to cellulose and used to absorb mid-region antibodies from a goat antiserum against intact human PTH. This assay has been applied to the measurement of circulating PTH in man: in normal subjects the concentration in serum ranged from undetectable (less than 40 pg/ml) to 70 pg/ml, the reference standard being the human PTH 28-54 peptide. In patients with primary hyperparathyroidism concentrations ranged from 120 to 1800 pg/ml. Hormone was not detected in patients with hypoparathyroidism. In normal subjects and in patients with primary hyperparathyroidism the mid-region PTH concentrations were similar to those obtained in an amino-terminal specific assay. By contrast, carboxy-terminal PTH concentrations were markedly higher being 10-fold greater in both groups studied. In patients with primary hyperparathyroidism undergoing parathyroidectomy and in chronic renal failure patients who were infused with calcium, mid-region and amino-terminal PTH disappeared much more rapidly than carboxy-terminal PTH. However, although mid-region PTH was initially cleared as quickly as amino-terminal PTH, it then reached a plateau and remained at a higher level. Thus the mid-region specific assay described here is proving to be of value in the study of the secretion and metabolism of PTH.

Calcium↗
PubMed1986

Localized conjunctival amyloidosis: case reports and review of literature.

Two men in their 20s had flat, stable, pink, well-vascularized conjunctival lesions found unexpectedly which on biopsy proved to be primary localized amyloidosis. The diagnosis was made possible by the absence of systemic manifestations or antecedent ocular disease, the presence of diffuse homogeneous connective tissue deposits and characteristic histochemical staining properties. The cases were remarkable for their color, texture, location, and presentation and suggest that a high index of suspicion, if not an alacrity to biopsy, is needed for the diagnosis of primary localized amyloid to be made.

Adult↗