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Biomedical subjects

G F Lee

Publications and source records attributed to G F Lee.

At least 19 recordsLinked to original sources
PubMed1995

Identification of functionally important helical faces in transmembrane segments by scanning mutagenesis.

We applied mutational analysis to a protein domain that functions in neither catalysis nor binding but, rather, in transmembrane signaling. The domain is part of chemoreceptor Trg from Escherichia coli. It contains four transmembrane segments, two from each subunit of the homodimer. We used cysteine scanning to investigate the functional importance of each of 54 residues in the two transmembrane segments. Cysteines at some positions resulted in subtle but significant reductions in tactic response. Those positions defined a specific helical face on each segment, implying that the segments function as helices. The functionally important faces corresponded to structural, helical packing faces identified independently by biochemical studies. All functionally impaired receptors exhibited altered signaling properties, either reduced signaling upon stimulation or induced signaling in the absence of stimulation. The distribution of substitutions creating these two phenotypes implied that conformational signaling involves movement between the two transmembrane helices within a subunit and that signaling is optimal when stable interactions are maintained across the interface between subunits.

Cell Membrane↗
PubMed1995

Transmembrane signaling characterized in bacterial chemoreceptors by using sulfhydryl cross-linking in vivo.

Transmembrane signaling by bacterial chemoreceptors is thought to involve conformational changes within a stable homodimer. We investigated the functional consequences of constraining movement between pairs of helices in the four-helix structure of the transmembrane domain of chemoreceptor Trg. Using a family of cysteine-containing receptors, we identified oxidation treatments for intact cells that catalyzed essentially complete sulfhydryl cross-linking at selected positions and yet left flagellar and sensory functions largely unperturbed. Constraining movement by cross-links between subunits had little effect on tactic response, but constraining movement between transmembrane segments of the monomer drastically reduced function. We deduce that transmembrane signaling requires substantial movement between transmembrane helices of a monomer but not between interacting helices across the interface between subunits.

Bacterial Proteins↗
PubMed1995

Quantitative approaches to utilizing mutational analysis and disulfide crosslinking for modeling a transmembrane domain.

The transmembrane domain of chemoreceptor Trg from Escherichia coli contains four transmembrane segments in its native homodimer, two from each subunit. We had previously used mutational analysis and sulfhydryl cross-linking between introduced cysteines to obtain data relevant to the three-dimensional organization of this domain. In the current study we used Fourier analysis to assess these data quantitatively for periodicity along the sequences of the segments. The analyses provided a strong indication of alpha-helical periodicity in the first transmembrane segment and a substantial indication of that periodicity for the second segment. On this basis, we considered both segments as idealized alpha-helices and proceeded to model the transmembrane domain as a unit of four helices. For this modeling, we calculated helical crosslinking moments, parameters analogous to helical hydrophobic moments, as a quantitative way of condensing and utilizing a large body of crosslinking data. Crosslinking moments were used to define the relative separation and orientation of helical pairs, thus creating a quantitatively derived model for the transmembrane domain of Trg. Utilization of Fourier transforms to provide a quantitative indication of periodicity in data from analyses of transmembrane segments, in combination with helical crosslinking moments to position helical pairs should be useful in modeling other transmembrane domains.

Amino Acid Sequence↗
PubMed1994

Deducing the organization of a transmembrane domain by disulfide cross-linking. The bacterial chemoreceptor Trg.

The transmembrane domain of chemoreceptor Trg from Escherichia coli contains four segments, two from each subunit of the homodimer. We used site-specific mutagenesis to introduce cysteines into those segments and oxidative cross-linking of cysteine pairs to identify residues that are near each other in space. Propensity for cross-linking was determined for pairs of homologously placed cysteines in the two subunits of the dimer at all 54 possible positions. Also, combinations of cysteines were identified that readily oxidized to join heterologous segments within or between monomers. These patterns of cross-linking were used to develop a model for the three-dimensional structure of the transmembrane domain in which the four transmembrane segments are helices associated in a bundle, with stronger interactions near the periplasm and weaker interactions near the cytoplasm. The striking similarity of this model to a model for the transmembrane domain of chemoreceptor Tar, derived using the same experimental strategy, strengthens the notion that a combination of comprehensive cysteine substitutions and analysis of patterns of disulfide cross-linking is sufficient to deduce a detailed three-dimensional structure for a transmembrane domain.

Bacterial Proteins↗
PubMed1991

Alternative liability insurance: a physician-owned captive insurance company.

The physician-owned captive insurance company is a lesser known but dynamic alternative to commercial insurance. The Physicians Reimbursement Fund, Ltd., was founded in 1975 in response to the malpractice crisis of that year. The company insures about 100 physicians in high-risk specialties. Approximately one half are obstetrician-gynecologists. Innovative management has enabled this company to operate successfully at a fraction of the premium charged by typical insurance companies. Fourteen years of experience have demonstrated the ability of this company to successfully serve the needs of the community.

Insurance, Liability↗
PubMed1989

Developmentally regulated proteolytic processing of a yolk glycoprotein complex in embryos of the sea urchin, Strongylocentrotus purpuratus.

We have isolated a yolk glycoprotein complex from eggs and early embryos of the sea urchin, Strongylocentrotus purpuratus. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of these complexes and peptide mapping of their individual glycoprotein components indicate that developmental stage-specific changes in molecular composition of the complex are due to proteolytic processing events. Our data revealed that a 180 kDa glycoprotein of the egg complex is separated by a single proteolytic cleavage into intermediate glycoproteins of 115 and 76 kDa early in development. By the hatched blastula stage, each of these intermediate glycoproteins has been further processed to lower molecular weight forms: the 115 kDa protein is proteolytically clipped to a 84 kDa form, perhaps through 110 and 105 kDa intermediaries, while the 76 kDa molecule is directly processed to a 65 kDa form.

Animals↗
PubMed1987

Fine-needle aspiration of the breast: the outpatient management of breast lesions.

Fine-needle aspiration of the breast has become a well-accepted diagnostic tool for the management of breast lesions. When employed on an ambulatory basis it is both accurate and cost-effective. This study of a series of patients managed over a 2-year period demonstrates the use of this technique in an ambulatory gynecologic practice. Results demonstrate this to be a very rapidly accomplished, effective procedure that is very well accepted by the patients. Results are generally available within 24 hours and permit both the physician and the patient to accurately predict the course of management. In addition, it allows the primary physician to accurately determine which patients will require in-hospital management and which may safely undergo ambulatory, office-based biopsy of solid lesions. Experience shows this to be a valuable diagnostic tool that can be safely utilized by the practicing gynecologist.

Adult↗
PubMed1984

Developing a hospital pharmacy purchasing system.

Suggestions for developing or modifying a pharmacy purchasing system are presented and discussed. To achieve an optimal purchasing system, pharmacy managers must understand the development and operation of their current systems and enlist the participation of other hospital departments in planning the new or modified system. A pharmacy purchasing system should ensure that drug products and supplies of the highest quality are obtained at the lowest price, that these items are available when needed, and that the financial investment in drug and supply inventory is appropriate. The job requirements, activities, and responsibilities of pharmacy purchasing personnel are described, and the recording and retrieving of purchasing data are discussed. Various order-placement alternatives are compared, and order-shipment alternatives are described. Equipment and supply requirements for the purchasing function are also presented. An efficient, productive purchasing system can produce cost savings for the pharmacy department and the institution.

Inventories, Hospital↗
PubMed1982

Alternative to the traditional discount method of wholesaler purchasing.

A program of purchasing drugs from wholesalers at the wholesaler's exact invoice cost plus a percentage is described and compared with the traditional method of average wholesale price (AWP) less a discount. The comparison was conducted by the pharmacy department of a 310-bed, teaching hospital that awarded a one-year contract to a wholesaler offering its items at the exact cost plus a pre-established percentage. Data collected from monthly wholesaler computer printouts gave the following information on each product: (1) list price per item, (2) actual cost to pharmacy per item, (3) percentage discount from AWP, and (4) quantity ordered. The net percentage discount from AWP for 12 months was calculated and compared to the former (traditional) discount rate. The net discount from AWP was 15.6% for purchases made by the hospital during the first 12 months of the program. When compared with the smaller discount the hospital traditionally received, the new program saved the hospital $5758 on annual purchases of $136,419. The actual dollar savings to an institution that changes from a traditional discount program to a cost-plus-percentage program depends on: (1) the negotiated percentage added to wholesaler cost, (2) the discount from AWP that the institution was previously receiving, and (3) the volume of wholesale purchases.

Pharmacy Service, Hospital↗