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Biomedical subjects

P Silver

Publications and source records attributed to P Silver.

At least 91 records · Page 5Linked to original sources
PubMed1983

Genetic mapping of the Escherichia coli leader (signal) peptidase gene (lep): a new approach for determining the map position of a cloned gene.

The gene for leader peptidase, termed lep, was mapped to the region between purI and nadB at min 54 to 55 on the Escherichia coli chromosome. Mapping involved (i) cloning the gene into the plasmid pBR322, (ii) transforming the plasmid into a polA strain where it cannot replicate autonomously, (iii) selecting by ampicillin resistance the rare cell in which the plasmid had recombined into the chromosome, and (iv) mapping the chromosomal site of drug resistance (and thus plasmid integration) by Hfr matings and P1 transduction. The map position was confirmed by an assay of the enzyme content of cells bearing an F' factor which covered that region of the chromosome.

Ampicillin↗
PubMed1982

The isolation of homogeneous leader peptidase from a strain of Escherichia coli which overproduces the enzyme.

Leader (signal) peptidases cleave the NH2-terminal leader sequences of newly synthesized secreted and membrane proteins during, or shortly after, they insert across the membrane. We have constructed a plasmid, pPS9, in which the structural gene for Escherichia coli leader peptidase is under transcriptional control of a lambda promoter, PR. pPS9 also codes for a temperature-sensitive lambda repressor, causing repression of expression of the plasmid leader peptidase gene at 30 degrees C and rapid synthesis of this enzyme at 42 degrees C. Under appropriate growth regimens, leader peptidase is overproduced 75-fold. Leader peptidase from this strain has been purified to homogeneity. It consists of a 37,000-dalton polypeptide which co-migrates with enzyme activity on DEAE-cellulose and chromatofocusing chromatography. Antibody to this leader peptidase is described.

DNA Restriction Enzymes↗
PubMed1981

Membrane assembly from purified components. I. Isolated M13 procoat does not require ribosomes or soluble proteins for processing by membranes.

The coat protein of coliphage M13 is an integral protein of the host-cell cytoplasmic membrane prior to its assembly into virions. It is initially synthesized as procoat, a soluble precursor with a 23 amino acid leader sequence at its amino terminus. 35S-labeled procoat accumulates during an in vitro translation reaction that contains 35S-methionine and RNA from M13-infected cells. Radiochemically pure procoat has been isolated from in vitro translation reactions by extraction into an organic solvent and gel filtration through Sephadex LH-60. Radiochemically pure procoat can be used as substrate in rapid and quantitative assays for leader peptidase and for leader peptide hydrolase, an enzyme that degrades the leader peptide after its release from procoat. Procoat solubility, digestion by leader peptidase and processing by membranes are affected by the presence of Mg2+ ion. Isolated procoat is soluble in water at low ionic strength and mildly alkaline pH as well as in detergent solutions. It is cleaved to coat protein by purified E. coli leader peptidase and by inverted E. coli inner-membrane vesicles. These properties of the purified procoat mirror those of the procoat in crude extracts. This suggests that there are no other soluble components that are necessary for the assembly of procoat into the membrane and its conversion to coat; specifically, it provides powerful evidence that protein synthesis is not involved.

Cell Membrane↗
PubMed1981

Membrane assembly from purified components. II. Assembly of M13 procoat into liposomes reconstituted with purified leader peptidase.

The major coat protein of coliphage M13 is an integral protein of the E. coli plasma membrane prior to its assembly into new virus particles. It is generated from its precursor, procoat, by a membrane-bound leader peptidase. We now describe the reconstitution of a highly purified preparation of this enzyme into vesicles of E. coli phospholipids. These vesicles bind procoat made in vitro and procoat isolated from in vitro synthesis. Both the crude and the purified substrates were converted post-translationally to coat protein. A significant proportion of the coat protein becomes inserted into the vesicle bilayer, with the N terminus facing the vesicle interior and the C terminus exposed to the external medium. These results strongly suggest that highly purified leader peptidase from E. coli and phospholipids are the only components necessary to mediate the binding, processing and insertion of this integral membrane protein.

Coliphages↗
PubMed1979

Histidyl and tyrosyl residue ionization studies of subtilisin Novo.

The low field portion of the 360 MHz 1H nuclear magnetic resonance spectrum of phenylmethanesulfonyl-subtilisin Novo (EC 3.4.21.14) has been studied as a function of pH. Analysis of the pH-induced chemical shift changes occurring between 6 to 7 ppm revealed five classes of ionizable residues with pK values (uncorrected) of 10.3, 10.7, 10.7, 10.8, and 11.0. With a single exception the titration curves can be fit by assuming a simple proton ionization equilibrium. Four classes of low intensity broad resonances, assigned to the histidyl residues, are observed between 8 and 9 ppm. Uncorrected pK values of 5.4, 5.7, 6.0, and 6.4 were determined for the residues comprising each of these classes. The spectral data are consistent with protonation of one or more histidyl residues upon acid induced denaturation of the protein. These results are compared with those of analogues studies performed by the use of other techniques.

Chemical Phenomena↗
PubMedDate not supplied

Evaluation of a portable blood gas analyzer for pediatric interhospital transport.

We evaluated a portable blood gas analyzer for its speed, reliability, and usefulness during interhospital transportation of critically ill children in a prospective study. The accuracy of a portable blood gas analyzer (PBGA) was first established by comparing its results with values obtained from a standard blood gas analyzer. The speed, accuracy, and usefulness of the PBGA were then compared with those of standard analyzers at 10 referring hospitals during interhospital transportation of critically ill children. A highly significant linear correlation was demonstrated between values obtained using the PBGA and those derived from standard analyzers. The time required to obtain blood gas results was 2 min with the portable device, significantly less than the mean of 8.4 min +/- 6.4 min (range 1-24 min) required to get results from the laboratory facilities of the referring hospitals. Modification of treatment or adjustment to mechanical ventilation was required in 30% of transported patients based on blood gas results obtained immediately before departure from the referring hospital. We conclude that a portable blood gas analyzer provides rapid, reliable, and useful data that help to determine therapy for critically ill children awaiting interhospital transport.

Blood Gas Analysis↗