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B A Levine

Publications and source records attributed to B A Levine.

At least 19 recordsLinked to original sources
PubMed1992

Insulin receptor tyrosine kinase domain auto-dephosphorylation.

We have observed dephosphorylation of the soluble, 48 kDa insulin receptor tyrosine kinase domain following its tyrosine autophosphorylation. Dephosphorylation was associated with generation of inorganic phosphate, thereby making catalysis by reversal of the kinase reaction unlikely. The kinase domain preparations could not be shown to contain detectable, contaminating protein tyrosine phosphatase activity. In addition, dephosphorylation was insensitive to protein phosphatase inhibitors. However, it was blocked by the kinase inhibitor staurosporine. These results are consistent with insulin receptor kinase domain auto-dephosphorylation via catalysis involving the kinase itself. These findings raise the possibility of a novel mechanism for termination of the insulin receptor signal.

Animals↗
PubMed1992

Interaction of calmodulin with phospholamban and caldesmon: comparative studies by 1H-NMR spectroscopy.

In order to identify comparative aspects of the interaction of calmodulin with its target proteins, proton magnetic-resonance studies of complex formation between calmodulin and defined segments of phospholamban and caldesmon have been undertaken. Residues 3-15 in the cytoplasmic region of phospholamban, an integral membrane protein of cardiac sarcoplasmic reticulum believed to regulate the calcium pumping ATPase, are shown to contribute to interaction with calmodulin. Using wheat germ calmodulin specifically modified with a spin-label to provide the spectral means for spatial localisation, these residues of phospholamban were correlated with binding in the vicinity of the probe attached to Cys-27 in the N-terminal domain of calmodulin. This interaction, relevant to the mechanism of calmodulin-dependent phosphorylation of phospholamban that relieves its inhibitory influence on the calcium pump, provides a useful model system for comparative study of the properties of calmodulin-binding domains. We contrast here a calmodulin-binding segment in the C-terminal region of caldesmon localised by 1H-NMR study of the interface(s) between the two proteins. These observations are discussed in the context of other calmodulin-binding sequences.

Amino Acid Sequence↗
PubMed1992

Binding sites involved in the interaction of actin with the N-terminal region of dystrophin.

Two actin-binding sites have been identified on human dystrophin by proton NMR spectroscopy of synthetic peptides corresponding to defined regions of the polypeptide sequence. These are Actin-Binding Site 1 (ABS1) located at residues 17-26 and Actin-Binding Site 2 (ABS2) in the region of residues 128-156. Using defined fragments of the actin amino acid sequence, ABS1 has been shown to bind to actin in the region represented by residues 83-117 and ABS2 to the C-terminal region represented by residues 350-375. These dystrophin-binding sites lie on the exposed domain in the actin filament.

Actins↗
PubMed1992

A comparison of case retrieval times: film versus picture archiving and communications systems.

One of the advantages that a picture archiving and communications system (PACS) is supposed to provide over a film-based operation is improved performance in retrieving images. Although it seems self-evident that this should be so, this experiment was intended to verify this and to provide some time comparisons for the two methods. The experiment consisted of randomly selecting ultrasound and computed tomography cases and determining how long it took to retrieve files at a PACS workstation or in person from the file room. To simulate actual retrieval volumes, a total of 40 cases from current to 6 months old, 20 cases from the past year, and 10 cases more than 1 year old was selected. Results indicate that PACS retrieval can indeed be faster than file room retrieval. However, the difference is less for recent cases than for older cases. For cases 6 or fewer months old, the workstation retrieval was approximately 2.5 minutes faster per case than the film file room. This time difference increased markedly when extended to the 1-year and older-than-1-year groups. This report details the results of this study and provides information about the reliability of the two archives.

Filing↗
PubMed1992

Multiple binding sites on the CH2 domain of IgG for mouse Fc gamma R11.

Important mammalian defensive functions such as phagocytosis are triggered in leukocytes by the interaction of the Fc region of IgG with cell surface receptors (Fc gamma R). The CH2 domain of IgG has been implicated previously as the site of interaction with human and mouse Fc gamma R. This domain was mapped for interaction with mouse Fc gamma R11 expressed by the macrophage-like cell line P388D1, using two panels of a total of 32 site-directed mutants of mouse IgG2b and chimeric human IgG3 monoclonal antibodies. Two potential binding sites have been identified: one in or within the vicinity of the lower hinge site on IgG for human Fc gamma R1, and one within the binding site on IgG for Clq. The three mutant IgGs (Gly 237----Ala, Asn 297----Ala, and Glu 318----Ala) which do not interact in complexed form also fail to bind as monomers. A 1H NMR study of the three non-binding monomeric mutants suggests that the mutations are largely site-specific, indicating that IgG interacts with mouse Fc gamma R11 at two regions within the CH2 domain. This interaction dictates phagocytosis mediated by Fc gamma R11 of the P388D1 cell line.

Animals↗
PubMed1992

Role of platelet-activating factor in hepatic responses after bile duct ligation in rats.

Role of platelet-activating factor (PAF) as a potential mediator of hepatic pathophysiology was investigated using a rat model of obstructive jaundice. Over a 1-wk course of bile duct ligation, a sixfold increase in tissue levels of PAF (1.57 +/- 0.43 ng/g vs. control 0.24 +/- 0.08 ng/g) occurred in the liver, whereas no change was observed in PAF levels in plasma. Concomitantly, endotoxin was detected in portal blood drawn from jaundiced rats, and antagonism of the putative effect of endotoxin by neomycin plus polymyxin B reduced local PAF concentrations in livers from jaundiced animals. Induction of neutropenia failed to alter the elevated hepatic PAF concentrations. Moreover, a large quantity of PAF was released spontaneously from Kupffer cells isolated from livers derived from jaundiced rats but not from endothelial cells or hepatocytes from the same animals. An in vitro study using cultured Kupffer cells from normal rats indicated that Kupffer cells secreted a significant amount of PAF in response to lipopolysaccharide challenge; pretreatment of cells with polymyxin B prevented this stimulated PAF release. Treatment of animals with either of two PAF receptor antagonists (BN 52021 and WEB 2170) partially prevented the increase in tissue levels of eicosanoids and O2-derived free radicals and partially alleviated liver injury as judged by the appearance of glutamate-pyruvate transaminase in the plasma of jaundiced rats. The present study indicates 1) that endogenous PAF may be an important signaling mediator for the hepatic inflammatory alterations associated with short-term bile duct ligation and 2) that the interaction of Kupffer cells with portal endotoxin is the mechanism by which PAF is produced locally.

Animals↗
PubMed1992

The role of endoscopic sclerotherapy in the management of esophageal varices.

Endoscopic sclerotherapy of esophageal varices has gained worldwide popularity. There is a consensus that sclerotherapy is an effective treatment for temporarily controlling acute variceal hemorrhage. Sclerotherapy has no place in the routine prophylaxis before the index bleed. The role of long-term sclerotherapy to prevent rebleeding is debatable. It is our bias that once patients with cirrhosis suffer a variceal hemorrhage, they should be considered for liver transplantation. If they are not suitable candidates for transplantation and have mild to moderate hepatic dysfunction, then portosystemic shunting provides definitive secondary prophylaxis against rebleeding. Sclerotherapy should be reserved for patients with advanced decompensated cirrhosis.

Acute Disease↗
PubMed1992

Inflammation and platelet-activating factor production during hepatic ischemia/reperfusion.

The role of platelet-activating factor as a potential mediator of hepatic inflammatory injury associated with liver ischemia/reperfusion was investigated using a partial no-flow model in rats in vivo. Platelet-activating factor levels of livers from sham-operated rats and from animals experiencing hepatic reperfusion for less than 6 hr were very low. They were observed to increase significantly after 12 hr of reperfusion and reached peak levels after a 24-hr reperfusion period, a time when maximal hepatic injury and inflammation occurred. Treatment of experimental rats with WEB2170, a platelet-activating factor receptor antagonist, attenuated the hepatic injury and inflammation, as evidenced by decreases in plasma ALT and in hepatocyte necrosis and neutrophil infiltration. Both inactivation of Kupffer cells with gadolinium chloride and inhibition of the formation of reactive oxygen species with allopurinol reduced platelet-activating factor production in the liver, whereas induction of neutropenia had no effect, suggesting that interaction of Kupffer cells with oxygen-derived free radicals may be a plausible mechanism for hepatic platelet-activating factor accumulation. It is concluded that platelet-activating factor contributes to the inflammatory consequences of ischemia/reperfusion underlying late-phase hepatic injury.

Alanine Transaminase↗
PubMed1992

Role of platelet-activating factor in pancreatitis-associated acute lung injury in the rat.

Acute necrotizing pancreatitis induced by infusion of bile salt into the pancreatic duct in rats is consistently associated with acute lung injury similar to the adult respiratory distress syndrome. The role of platelet-activating factor (PAF) in this pancreatitis-associated remote organ failure (lung injury) was investigated. Pulmonary tissue levels of PAF were increased gradually and reached a level of 1345 +/- 455 pg/g (6 times the control level) at 12 hours after induction of pancreatitis, whereas pancreatic PAF levels were undetectable and blood PAF remained unchanged. This local pulmonary PAF accumulation occurred at approximately the same time as the progression of lung injury. Pulmonary responses detected (i.e., eicosanoid production, leukocytic infiltration, Evan's blue extravasation, beta-glucuronidase release) were attenuated to varying degrees by treatment of rats in which pancreatitis was initiated with the PAF receptor antagonists (WEB2170 and BN52021). Rat lung lavages were examined after a 12-hour course of pancreatitis and no changes in PAF concentration, surfactant content, and phospholipase A2 (PLA2) activity were noted. Intravenous administration of PLA2 promoted pulmonary PAF production in experimental rats with pancreatitis but not in normal rats. This observation indicates that PLA2, which was determined to be elevated in plasma during pancreatitis, may be responsible for the accumulation of PAF in the lung. In conclusion, pancreatitis-associated lung injury appears to result from an endogenous inflammatory response in which PAF may play an important role.

Animals↗
PubMed1992

Variceal hemorrhage associated with portal vein thrombosis: treatment with a unique portal venous stent.

A patient with an uncommon cause of portal venous hypertension, pancreatitis, is depicted. The patient had an equally uncommon pattern of symptoms and signs consisting of abdominal pain and lower gastrointestinal hemorrhage caused by colonic varices. A unique treatment, with angiographic placement of an expandable intraluminal stent within the portal vein, was employed to reopen the portal venous system and reduce portal pressure. Relief of bleeding was accomplished and sustained for more than 1 year.

Gastrointestinal Hemorrhage↗
PubMed1991

Autophosphorylation of soluble insulin receptor protein-tyrosine kinases. 1H NMR spectral changes observed during phosphorylation of mobile tyrosine residues.

Autophosphorylation of a soluble approximately 48-kDa derivative of the insulin receptor protein-tyrosine kinase occurs at multiple tyrosine residues (analogous to tyrosines 1158, 1162, and 1163 in the kinase homology region of the native receptor and tyrosines 1328 and 1334 in the carboxyl-terminal tail) and is accompanied by an increase in the specific activity of the enzyme toward exogenous substrates. A comparison of 1H NMR spectra of approximately 48- and approximately 38-kDa forms of enzyme (the latter generated by tryptic deletion of approximately 10 kDa from the carboxyl terminus of the approximately 48-kDa protein) allows a correlation of observed mobile tyrosine resonances to two of the known sites of autophosphorylation (residues 1328 and 1334). Furthermore, spectra acquired during autophosphorylation of the approximately 48-kDa enzyme reveal a rapid downfield shift in the resonances of these mobile tail tyrosines consistent with their phosphorylation (as confirmed by two-dimensional tryptic phosphopeptide mapping performed under identical conditions). This experimental strategy now provides a means by which to monitor protein-tyrosine kinase autophosphorylation in solution in real time.

Amino Acid Sequence↗
PubMed1991

Deletion of approximately 10 kDa from the carboxyl terminus of a soluble approximately 48-kDa insulin receptor protein-tyrosine kinase results in slower rates of diphosphorylation of a series of dodecapeptide substrates. An assessment by 1H NMR.

Autophosphorylation of a soluble approximately 48-kDa derivative of the insulin receptor protein-tyrosine kinase is accompanied by an increase in its specific activity towards exogenous substrates. In the present study, we have utilized 1H NMR to compare the order and rate of mono- and diphosphorylation of multiple tyrosine residues in a series of synthetic dodecapeptide substrates (based on the receptor sequence, which includes major sites of autophosphorylation (RRDIYETDYYRK), with substitution(s) at positions 6 and/or 7 based on residue size and/or charge) by the approximately 48-kDa enzyme and by a approximately 38-kDa enzyme generated by tryptic deletion of approximately 10 kDa from the carboxyl terminus of the approximately 48-kDa protein. Both enzymes exhibit a marked order and progression of phosphorylation of peptide tyrosine residues; for each peptide, phosphorylation initiates and proceeds to completion first on tyrosine 9, followed by phosphorylation on tyrosine 10. Although removal of the carboxyl terminus does not affect the rate of monophosphorylation of these peptides on tyrosine 9, the smaller enzyme exhibits a slower rate of diphosphorylation (at tyrosine 10), as compared with the approximately 48-kDa enzyme.

Amino Acid Sequence↗
PubMed1991

A soluble insulin receptor kinase catalyzes ordered phosphorylation at multiple tyrosines of dodecapeptide substrates.

At present, the requirements for efficient phosphorylation of exogenous substrates by protein-tyrosine kinases are largely unknown. The proton resonances of each of the 3 tyrosines of the dodecapeptide substrate RRDIYETDYYRK are well resolved in the aromatic region of the 1H NMR spectra: thus, it is feasible to directly monitor phosphorylation at each site. A soluble approximately 48-kDa derivative of the human insulin receptor cytoplasmic protein-tyrosine kinase domain phosphorylates this peptide at all 3 tyrosine sites and does so in a highly ordered and progressive manner (Y9, then Y10 and finally Y5), proceeding to full stoichiometry at each site before phosphorylating the next. This experimental system now provides an approach by which to follow the stereochemical requirements and dynamics of substrate phosphorylation by a protein-tyrosine kinase in solution in real time.

Amino Acid Sequence↗
PubMed1991

Biliary pancreatitis. Operative outcome with a selective approach.

To evaluate the efficacy of a selective approach to biliary pancreatitis, we reviewed the outcomes in 276 consecutive patients undergoing operations for this diagnosis during a 7-year period. Initial conservative therapy resulted in elective operations in 63% and urgent operations in 37%. Only 10 patients (3.6%) required primary pancreatic operations, 50% of them as emergencies. The proportion of common duct surgical explorations fell from 70% of those operated immediately after hospital admission to 20% by the third hospital day. Overall mortality was 1.8% but was increased to 30% in patients having an initial pancreatic operation. We conclude that a selective approach to biliary pancreatitis allows the operation to be performed electively in most patients and is associated with a low mortality and an acceptable length of stay. Most common duct stones pass spontaneously permitting cholecystectomy alone.

Acute Disease↗
PubMed1991

Glucose intolerance and hyperinsulinemia of cirrhosis are not results of spontaneous or surgical portosystemic shunting.

To assess if spontaneous portosystemic shunting from collaterals contributes to the hyperinsulinemia of cirrhosis, 12 patients with alcoholic cirrhosis underwent a 5-hour oral glucose tolerance test 1 day before and 10 days after an elective side-to-side portacaval shunt. The glucose, insulin, and C peptide responses to oral glucose post-shunt were exaggerated but comparable to preoperative values. Compared with preoperative values, the fasting molar ratio of C peptide to insulin postoperatively had increased 40% (6.0 +/- 1.2 versus 8.4 +/- 0.7), indicating improved hepatic function. These results suggest that extrahepatic portosystemic shunting secondary to spontaneous splanchnic collaterals plays little or no role in the hyperinsulinemia of cirrhosis. It appears that decreased hepatic degradation of insulin in these patients is secondary to hepatocellular dysfunction rather than a result of shunting of portal blood around the liver.

Adult↗
PubMed1991

Variceal rebleeding after portosystemic shunting. Strategies and solutions to a vexing problem.

The purpose of this review was to discuss an approach to the treatment of recurrent bleeding from esophageal or gastric varices after portosystemic shunt. From our own clinical experience, as well as that of others, it appears that re-establishment of portal decompression should offer the best chance at long-term survival. Luckily, innovations in angiographic technique have allowed attainment of this goal without the inordinate risk of an operative procedure. However, not all patients' situations will be amenable to such treatment. For some of them, operative decompression of the portal venous system can be carried out in an anatomic area previously untouched. For those patients in whom no decompression is possible, direct endoscopic treatment of the varices will offer an alternative, albeit temporizing, approach.

Combined Modality Therapy↗