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Biomedical subjects

L Lin

Publications and source records attributed to L Lin.

At least 415 records · Page 23Linked to original sources
PubMed1977

Molecular alterations of interferons.

Interferons can be chemically and enzymatically altered to obtain molecular forms which differ in size, charge, and/or host-range from native interferons. These data suggest that small active cores of interferons can be obtained which may possess more desirable characteristics than native interferons, such as lack of "species-specificity"" and increased stabilities. Studies for assessing alterations of interferons due to chemical or enzymatic treatments must monitor the treated interferons for changes in ratios of each of the various activities attributed to native interferons and must characterize the altered interferons in terms of each of the physical and biological markers.

Animals↗
PubMed1976

The carbamate reaction of glycylglycine, plasma, and tissue extracts evaluated by a pH stopped flow apparatus.

We have used a stopped flow rapid reaction pH apparatus to investigate the carbamate equilibrium in glycylglycine solutions and in three biological tissues, human plasma, sheep muscle, and sheep brain, as well as to investigate the kinetics of carbamate formation in glyclyglycine solution and in human plasma. The rapid reaction apparatus was equipped with a pH sensitive glass electrode in order to follow the time course of pH from 0.005 to 100 s after rapid mixing of a solution of amine or protein and CO2. Two phases of the pH curve were observed: a fast phase representing carbamate formation, and a slow phase due to the hydration of CO2 which was uncatalyzed since a carbonic anhydrase inhibitor was added to the biological solutions. From the time course of pH change during the fast phase K2, the R-NH2 ionization constant, and Kc, the carbamate equilibrium constant as well as the velocity constant for the formation of carbamate, ka could be calculated from data at different pH and pCO2. The carbamate formed in glycylglycine solutions over a wide range of pH and pCO2 was found consistent with the theory of carbamate formation and with published data. At ionic strength 0.16 and 37 degrees pK is 7.67. pKc 4.58. The heat of the carbamate reaction (deltaH) was calculated to be -3.2 kcal/mol between 20 degrees and 37 degrees. Kt of glycylglycine depends quantitatively on ionic strength as predicted by the Debye-Huckel theory. With ionic strength 0.16 ku was found to be 2,500 M1 S1 at 37 degrees. The activation energy of carbamate formation is 6.7 kcal/mol. Carbamate measurements in human plasma at pCO2 from 38 to 359 Torr. pH from 6.9 to 8.3, temperature 37 degrees, and ionic strength 0.15 provided evidence that two kinds of amino groups participate in carbamate formation. From the equilibrium constants computed for the two species they could be identified as alpha- and epsilon-amino groups. On the basis of a protein molecular weight of 69.000. 0.6 alpha-amino groups/molecule with pKz=7.0 and pKc=4.2, and 5.9 epsilon-amino groups/molecule with pKz=9.0 and pKc=4.3 contribute to carbamate formation. The velocity constant ka was estimated to be 4,950 M1 S1 for the alpha-amino groups and 13,800 M1 S1 for the epsilon-amino groups. Under physiological conditions (pCO2=40 Torr. pH=7.4). The concentration of carbamate in plasma is 0.6 mM and the half-time of carbamate formation is 0.05 s. In extracts prepared from sheep brain at 37 degrees pH=7 and pCO2=35 Torr. the carbamate formation was estimated to be 0.8 mM. With pCO2=70 Torr and the same pH and temperature the carbamate concentration in muscle approximates 0.3 mM and increases to 7 mM as pH rises to 8. It is concluded that, as in plasma, a considerable number of epsilon-amino groups appear to be available for carbamate formation in these tissues.

Animals↗
PubMed1976

Binding interactions between radiolabeled Escherichia coli elongation factor G and the ribosome.

We have prepared homogeneous radiolabeled Escherichia coli Elongation Factor G (EF-G) and examined its interactions with the ribosome. In agreement with earlier indirect observations we found that in the presence of high concentrations of fusidic acid approximately equimolar amounts of [3H]EF-G and [alpha-32P]GDP are stably bound to the ribosome. In the absence of fusidic acid, we observed a previously undescribed nucleotide-independent binding interaction between EF-G and the ribosome. This binding is detectable by rapid elution on small gel columns but is not apparent when reactions are analyzed by sucrose density gradient sedimentation. With the exception of the fact that the nucleotide-independent binding of EF-G to ribosome is apparently unaffected even by high concentrations of fusidic acid, it shares many properties in common with that binding which occurs in the presence of GDP. Nucleotide-independent binding requires magnesium ion (10 to 20 mM ) and does not require a monovalent cation but is strongly inhibited by even moderate concentrations of NH4Cl. This binding requires the presence on the ribosome of Protein L7/L12 and is inhibited by the antibiotic thiostrepton. Although we were unable to examine the binary ribosome.EF-G complex by equilibrium means, the observed stoichiometry under the conditions we employed did not exceed 0.2 mol of EF-G/mole of ribosome. Nonequilibrium measurements revealed that one-half of the EF-G was bound at a ribosome concentration of about 50 muM.

Binding Sites↗
PubMedDate not supplied

Biocompatibility test procedures for materials evaluation in vitro. II. Objective methods of toxicity assessment.

Methods of assessing the biocompatibility of materials for use in medical devices were evaluated. Ten materials were tested using quantitative, objectively graded in vitro biochemical and functional assays employing four cell lines (CCL 1, 74, 76, and 131) used in previous work and five primary cell types (human lymphocytes, polymorphonuclear leukocytes, and mixed leukocytes, mouse macrophages, and mouse embryo). The biochemical methods (DNA synthesis, protein synthesis, and ATP activity) demonstrated good agreement in toxicity ranking of the materials, regardless of which cell culture was used and, also, the cell cultures responded similarly for each method. Methods that measured functional characteristics of cells (adhesion and phagocytosis) were highly sensitive but had low toxicity ranking agreement and reproducibility. Assays (defined as method and cell culture combinations) using cell lines were more reproducible than assays using primary cell types. Significant differences in sensitivity were noted among the assay systems for particular material types. The in vitro assays were more sensitive to differences in material composition than was a 90-day assay by subcutaneous implantation in rats.

Adenosine Triphosphate↗