Search PubMed⌕ Search

Biomedical subjects

S S Li

Publications and source records attributed to S S Li.

138 records · Page 8Linked to original sources
PubMed1979

Ultraviolet light induction of diphtheria toxin-resistant mutants of normal and xeroderma pigmentosum human fibroblasts.

The UV induction of diphtheria toxin-resistant (DTr) mutants in normal and xeroderma pigmentosum human fibroblasts has been quantitatively characterized. A concentration of diphtheria toxin at which DTr cells are cross-resistant to Pseudomonas aeruginosa exotoxin A was determined and used in the selection of resistant mutants. Recovery of mutants was not influenced by the presence of wild-type cell densities of 1-8 x 10(5) per 9-cm plate, indicating no metabolic cooperation exists, in contrast to what is seen in the selection of some other variant phenotypes. Expression periods for UV-induced mutations differed with the severity of mutagen treatment and cell strain used. A relatively long (10-15 days after UV treatment) expression period was required for the maximum recovery of DTr mutants. Maximum recovery was followed by a decrease in mutation frequency on subsequent days evaluated. An apparent linear dose response within the dose range used was observed for UV-induced mutations in both normal and xeroderma pigmentosum fibroblasts. Our results indicate that xeroderma pigmentosum fibroblasts have higher UV-induced mutation frequencies per unit UV dose but similar frequencies per unit survival compared to normal cells within the range of UV doses tested.

Cells, Cultured↗
PubMed1977

Molecular characterization of limulin, a sialic acid binding lectin from the hemolymph of the horseshoe crab, Limulus polyphemus.

The sialic acid binding lectin, limulin, was isolated by gel filtration and ion-exchange chromatography from the hemolymph of Limulus polyphemus. When the purified protein was characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the presence of beta-mercaptoethanol, two major protein bands were observed. These two bands, subsequently found to contain carbohydrate as well, corresponded to molecular weights of 25 000 and 27 000. Amino acid sequence analyses were performed on both the intact protein and isolated cyanogen bromide fragments. The following primary structural features were noted in the amino-terminal region of limulin: (1) the absence of histidine and alanine from the NH2-terminal 50 residues; (2) the presence of five of the total eight prolines of the molecule between positions 13 and 30; and (3) a possible carbohydrate attachment site consisting of only the amino acids proline and serine between residues 13 and 19. The resultsof cyanogen bromide cleavage studies confirmed the presence of 2 methionine residues per subunit, at positions 25 and 58 respectively. No sequence heterogeneity was observed in this study. While it is quite possible that limulin plays some role in the defense mechanisms of the horseshoe crab, there is no obvious sequence homology between this invertebrate lectin and vertebrate immunoglobulins.

Agglutinins↗
PubMed1977

Isolation and characterization of a low-molecular weight seed protein from Ricinus communis.

A seed protein with an apparent molecular weight of 5000 has been isolated and purified from Ricinus communis. This protein has a very high content of glutamine and an unusual ultraviolet absorption spectrum. The amino-terminal sequence of 22 residues determined by automatic Edman degradation is: NH2-Pro-Ser-Gln-Gln-Gly-Cys-Cys-Gly-Gln-Ile-Gln-Glu-Gln-Gln-Asn-Leu-Arg-Gln-Cys-Gln-Glu-Tyr-.

Amino Acid Sequence↗
PubMed1977

Structure and properties of a hybrid tryptophan synthetase of alpha chain produced by genetic exchange between Escherichia coli and Salmonella typhimurium.

Genetic exchange between the structural genes for the alpha chain of tryptophan synthetase [tryptophan synthase; L-serine hydro-lyase (adding indoleglycerol-phosphate), EC 4.2.1.20] of E. coli and S. typhimurium yielded recombinant genes that specified functional hybrid polypeptides. The alpha chains produced by three recombinants appeared to be identical but differed from those of E. coli and S. typhimurium by at least 27 and 8 amino acid residues, respectively. In vivo and in vitro tests of enzyme function suggest that the hybrid alpha chains are near-equivalent to their fully active parental proteins.

Amino Acids↗
PubMed1976

Chromatographic isolation of the hemagglutinin polypeptides from influenza virus vaccine and determination of their amino-terminal sequences.

The influenza virus hemagglutinin polypeptides, HA1 and HA2, have been purified by gel filtration in the presence of sodium dodecyl sulfate from a vaccine preparation of the recombinant strain Heq1N2. Use of this technique for purification of the hemagglutinin polypeptides eliminated the need for proteolytic agents for removal of the hemagglutinin from the virus particles and 100-300 mg of virus yielded 10-30 mg of viral protein per chromatographic cycle. Because proteolysis is not required to remove the spikes from the viral envelope, the envelope-embedded HA2 polypeptide was purified in its entirety for structural analysis. Amino-terminal sequence analysis of the smaller polypeptide, HA2, revealed a cyclic repetition of glycyl residues through the first 24 residues at every third to fourth position. The sequence through the first 10 residues was identical to that presented by Skehel and Waterfield for other type A influenza viruses [(1975) Proc. Nat. Acad. Sci. USA 72, 93-97]. The HA1 (Heq/) polypeptide, on the other hand, had different amino acids at three or four out of the first 10 residues of the amino-terminal sequence when compared to HA1 from H0, H1, or H2 subtypes (Skehel and Waterfield). The present study has demonstrated the feasibility of the use of vaccine virus as a source of large quantities of viral protein for determination of primary structure.

Amino Acid Sequence↗
PubMedDate not supplied

How well do consumers understand percentage daily value on food labels?

One hundred four adults completed a multiple choice food label comprehension questionnaire and a food frequency questionnaire. Most respondents were able to accurately rate the fat content of five different foods using only the food label information. However, some underestimated food content for some foods. Also, only 29% correctly selected the definition of % daily value for fat (%DV), as "percent of the maximum daily recommended amount of fat."

Adult↗