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Biomedical subjects

P Walter

Publications and source records attributed to P Walter.

At least 343 records · Page 19Linked to original sources
PubMed1982

A bacterial secretory protein requires signal recognition particle for translocation across mammalian endoplasmic reticulum.

In vitro transcription of DNA from plasmid pBR322 was coupled to cell-free translation in a wheat germ system. The major translation product was pre-beta-lactamase. Upon addition of dog pancreas microsomes, the precursor was processed to authentic beta-lactamase as shown by partial NH2-terminal sequence analysis. Processing was linked to translocation into the microsomal vesicles. Salt-extracted microsomes did not process pre-beta lactamase but could be reactivated by purified signal recognition particle, which is the functional component of the salt wash (Walter, P., and Blobel, G. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 7112-7116). Signal recognition particle alone caused a drastic translation arrest that could be released by salt-depleted membranes. These data are consistent with those obtained for eukaryotic proteins and suggest that co-translational translocation of both bacterial and eukaryotic secretory proteins across the endoplasmic reticulum require identical components.

Animals↗
PubMed1982

Signal recognition particle contains a 7S RNA essential for protein translocation across the endoplasmic reticulum.

In addition to its previously characterized, six different polypeptide components, signal recognition protein--which functions in protein translocation across and integration into the endoplasmic reticulum membrane--contains a 7S RNA molecule. The RNA is closely identified with the small cytoplasmic 7SL RNA and is required for both structural and functional properties of signal recognition protein--which we therefore rename signal recognition particle.

Animals↗
PubMed1982

Gluconeogenesis in vitro. Formation of glucose 6-phosphate from malate by a cell-free rat-liver system consisting of cytosol and mitochondria.

A cell-free system prepared from rat liver containing cytosol and mitochondria as well as a number of cofactors at near physiological concentrations was shown to form glucose 6-phosphate from malate + 3-phosphoglycerate at a rate of 1.11 +/- 0.09 mumol . min-1 . g liver-1 (mean +/- SEM, n = 9, 30 degrees C). At least 70% of glucose 6-phosphate formed was derived from malate as calculated from experiments with [U-14C]malate. The indicated rates were measured between 10 min and 30 min incubation time when the system was near steady state with respect to the lactate/pyruvate ratio and to most of the gluconeogenic intermediates. In the absence of mitochondria, the rate of formation of glucose 6-phosphate from malate was about seven times lower than in their presence. A comparison between incubations carried out in presence or absence of mitochondria revealed that mitochondria decreased the lactate/pyruvate ratio and increased the ratio of (ATP + ITP)/(ADP + IDP). It could be shown that under the present incubation conditions, formation of glucose 6-phosphate was closely linked to the ratio of (ATP + ITP)/(ADP + IDP) whereas changing redox ratios had little influence on the gluconeogenic rate.

Animals↗
PubMed1982

Beneficial effects of adrenergic blockade in patients with subarachnoid haemorrhage.

A total of 148 patients presenting within 48 hours of subarachnoid haemorrhage were assigned at random to receive standard management only or standard management and treatment with the adrenergic-blocking agents propranolol and phentolamine (or propranolol alone) for three weeks. One hundred and thirty-four patients completed the study. Assessment at four weeks showed a strong trend for less neurological deficit in the treated group, almost statistically significant (p=0.053) in the women. During the first month the treated group suffered fewer episodes of clinical deterioration consistent with cerebral arterial spasm: thus more treated patients underwent operation and those who did had a better outcome (p=0.030). At one year fewer were dead or disabled (unable to work) in the treated group; a significant difference for women (p=0.030). Possible mechanisms for these actions may include a reduction in pulmonary oedema, prevention of myocardial infarcts, a reduction in plasma renin activity, nd a reduction in cerebral oxygen requirements. It is concluded that early adrenergic blockade benefits patients (particularly women) with subarachnoid haemorrhage for up to one year in terms of lesser neurological deficit. Beta-blocker rather than alpha-blockade appears to be the useful component. A randomised, blind extension of the present study using long-acting propranolol and placebo has shown a significant (p=0.026) decrease in deaths and significantly (p=0.003) fewer poor results in the treatment group.

Adolescent↗
PubMed1982

Chromoblastomycosis. A morphological investigation of the host-parasite interaction.

Chromoblastomycosis is a distinct cutaneous mycotic infection. Histologically it is characterized by the presence of fungus invariably in the yeast phase and by macrophages in large numbers. The morphology of fungus in both yeast and hyphal phases and its interaction with mononuclear phagocytes were examined using ultrastructural techniques. The major structural difference between the fungus in cutaneous tissue and that from a culture medium was a striking increase in cell wall thickness in the former. In the skin, the organisms were phagocytised by macrophages and enclosed in large membrane limited intracytoplasmic vacuoles. The thick, stratified, electron-dense fungal cell wall was observed in stages of alteration of varying severity. Most common was a granular modification of the outermost layers of the cell wall in contact with the vacuolar content. Fragmentation, splitting and rupture of this and deeper layers was also seen. Several ultrastructural features suggested that cell wall damage resulted from an active host cell digestion. The cell wall changes were in sharp contrast with the usual normal fungal cytoplasmic appearance. Only rare intracellular debris which we supposed to represent dead yeast cells were found. These findings suggested that the yeast responsible for chromoblastomycosis resisted fungicidal activities of cutaneous macrophages which possessed the ultrastructural features of stimulated phagocytes.

Chromoblastomycosis↗
PubMed1982

The placental lesions in congenital syphilis. A study of six cases.

Placentas from six mothers with serological tests suggestive of recent syphilitic infection and whose babies were suspected of being or proven to be infected by Treponema pallidum are described. One placenta from this series was large, bulky and pale, while the other 5 were without remarkable gross features. In all cases, the associated histological lesions were 1) hypercellular areas in the terminal and stem villi and 2) a focal peri- and/or intravillous polymorphonuclear concentration with or without necrosis. The former change which was the most frequent was characterized by an apparent increase of villous stromal cells, ultrastructurally identified as mesenchymal cells and Hofbauer cells. In addition, numerous fetal monocytes were found in the villous vascular lumina. The findings described here and in the literature suggest that congenital syphilis is associated with a spectrum of placental changes. We believe that these changes depend on the immunological reaction of the fetus. According to the sequence of events described in untreated patients, we distinguish two morphological phases: 1) an inductive phase without placental changes and 2) a reactive phase characterized by a predominantly lymphocytic inflammatory infiltration of the villi, followed by a reaction of mononuclear phagocytes.

Chorionic Villi↗
PubMed1982

Effect of intraaortic balloon counterpulsation (IABP) on myocardial infarct size and collateral flow in an experimental dog model.

To determine the influence of IABP on infarct size and collateral blood flow in each of 12 openchest anaesthetised mongrel dogs two small branches of the left coronary artery were occluded consecutively. The perfusion areas of both branches were comparable in size. IABP was started immediately before ligation of the first branch for a 90-min period followed by a reperfusion period of 90 min. Subsequently the second vessel was also occluded for 90 min as a control without IABP while myocardial oxygen consumption remained constant and was then reperfused. Infarct size was expressed as a percentage of the perfusion area. A difference in infarct size with and without IABP (18 +/- 17, 18 +/- 10% respectively) could not be observed. However a significant increase of collateral blood flow due to IABP in the subendocardial layer from 8.9 +/- 4.8 to 14.9 +/- 4.6 ml/100 g/min (p less than 0.05) was prevalent. In the subepicardial layer the augmentation from 23.7 +/- 19.9 to 26.9 +/- 15.2 was not significant. Thus, in spite of a small increase of collateral blood flow in the subendocardial layer of the ischemic myocardium the infarct size was not reduced by IABP in our dog model.

Animals↗
PubMed1982

Signal recognition protein is required for the integration of acetylcholine receptor delta subunit, a transmembrane glycoprotein, into the endoplasmic reticulum membrane.

Purified Signal Recognition Protein (SRP) has previously been shown to be required for the translocation of secretory proteins across the microsomal membrane (Walter and Blobel, 1980. Proc. Natl. Acad. Sci. U. S. A. 77:7, 112-7, 116) and to function in the early events of this process (Walter and Blobel, 1981. J. Cell Biol. 91:557-561). We demonstrate here that the delta subunit of acetylcholine receptor (AChR-delta), a transmembrane glycoprotein, likewise requires SRP for its asymmetric integration into microsomal membranes. We further demonstrate by partial sequence analysis that AChR-delta is synthesized with a transient NH2-terminal signal sequence of 21 residues that is cleaved off during integration into microsomal membranes. Integration of AChR-delta into the microsomal membrane vesicles proceeded asymmetrically, yielding a large (44 kdalton) core-glycosylated domain, inaccessible to externally added proteolytic enzymes and a smaller (approximately 16 kdalton) domain exposed on the outside of the vesicles and accessible to externally added proteolytic enzymes. The NH2 terminus of the molecule is contained in the 44-kdalton domain.

Amino Acid Sequence↗
PubMed1982

Protein translocation across the endoplasmic reticulum. I. Detection in the microsomal membrane of a receptor for the signal recognition particle.

Salt-extracted microsomal membranes (K-RM) contain an activity that is capable of releasing the signal recognition particle (SRP)-mediated elongation arrest of the synthesis of secretory polypeptides (Walter, P., and G. Blobel, 1981, J. Cell Biol., 91:557-561). This arrest-releasing activity was shown to be a function of an integral microsomal membrane protein, termed the SRP receptor (Gilmore, R., P. Walter, and G. Blobel, 1982, J. Cell Biol., 95:470-477). We attempted to solubilize the arrest-releasing activity of the SRP receptor by mild protease digestion of K-RM using either trypsin or elastase. We found, however, that neither a trypsin, nor an elastase "solubilized" supernatant fraction exhibited the arrest-releasing activity. Only when either the trypsin- or elastase-derived supernatant fraction was combined with the trypsinized membrane fraction, which by itself was also inactive, was the arrest-releasing activity restored. Release of the elongation arrest was followed by the translocation of the secretory protein across the microsomal membrane and the removal of the signal peptide. Thus, although we have been unable to proteolytically sever the arrest-releasing activity from K-RM and thereby to uncouple the release of the elongation arrest from the process of chain translocation, we have been able to proteolytically dissect and reconstitute the arrest-releasing activity. Furthermore, we found that the arrest-releasing activity of the SRP receptor can be inactivated by alkylation of K-RM with N-ethylmaleimide.

Endoplasmic Reticulum↗
PubMed1982

Protein translocation across the endoplasmic reticulum. II. Isolation and characterization of the signal recognition particle receptor.

The signal recognition particle (SRP)-mediated elongation arrest of the synthesis of nascent secretory proteins can be released by salt-extracted rough microsomal membranes (Walter, P., and G. Blobel, 1981, J. Cell Biol, 91:557-561). Both the arrest-releasing activity and the signal peptidase activity were solubilized from rough microsomal membranes using the nonionic detergent Nikkol in conjunction with 250 mM KOAc. Chromatography of this extract on SRP-Sepharose separated the arrest-releasing activity from the signal peptidase activity. Further purification of the arrest-releasing activity using sucrose gradient centrifugation allowed the identification of a 72,000-dalton polypeptide as the protein responsible for the activity. Based upon its affinity for SRP, we refer to the 72,000-dalton protein as the SRP receptor. A 60,000-dalton protein fragment (Meyer, D. I., and B. Dobberstein, 1980, J. Cell Biol., 87:503-508) that had been shown previously to reconstitute the translocation activity of protease-digested membranes, was shown here by peptide mapping and immunological criteria to be derived from the SRP receptor. Findings that are in part similar, and in part different from these reported here and in our preceding paper were made independently (Meyer, D. I., E. Krause, and B. Dobberstein, 1982, Nature (Lond.). 297:647-650) and the term "docking protein" was proposed for the SRP receptor. A lower membrane content of both SRP and the SRP receptor than that of membrane bound ribosomes suggests that the SRP-SRP receptor interaction may exist transiently during the formation of a ribosome-membrane junction and during translocation.

Centrifugation, Density Gradient↗