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Biomedical subjects

R Chen

Publications and source records attributed to R Chen.

At least 577 records · Page 32Linked to original sources
PubMed1983

Dietary saturated fatty acid content affects lymph lipoproteins: studies in the rat.

We examined effects on intestinal absorption of cholesterol and triglycerides and intestinal lipoprotein formation by feeding rats diets in which saturated fatty acids (palmitic plus stearic) comprised 78%, 68%, 48%, or 38% of triglyceride fatty acids. Absorption into lymph of radiolabeled cholesterol was proportional to triglyceride absorption. The rates of absorption of these lipids were related inversely to the % saturated fatty acids fed. The distribution of newly absorbed cholesterol and triglyceride into intestinal lipoproteins differed. With increasing cholesterol absorption more was recovered in very low density lipoproteins in contrast to the appearance preferentially in chylomicrons of larger quantities of fatty acid. Lymph lipid content did not reflect a consistent pattern in relation to the experimental diet fed. The fatty acid composition of triglyceride-rich lymph lipoproteins resembled the diet closely. One-quarter of the intestinal lymph particles from rats fed the highly saturated diets was flattened and polygonal as judged by electron microscopy if cooled to room temperature; whereas with the same diets, particles collected and isolated at 37 degrees C were round. Proportions of A-I and C apolipoproteins in triglyceride-rich intestinal particles varied inversely; apoA-I increased as fat/cholesterol absorption was greater. Diet-induced alterations in plasma lipoproteins and increased circulating triglycerides in this study in rats were unrelated to the variations in intestinal absorption or lymph lipoprotein formation.

Animals↗
PubMed1982

Primary structure of major outer-membrane protein I (ompF protein, porin) of Escherichia coli B/r.

In the outer membrane of Gram-negative bacteria hydrophilic pores exist, allowing the diffusion of various low-molecular-weight solutes. These pores are formed by proteins, the porins. In a preliminary communication [Chen, Krämer, Schmidmayr & Henning (1979) Proc. Natl. Acad. Sci. U.S.A. 76, 5014-5017] we presented the primary structure of one of these porins, the 340-amino-acid-residue protein I (ompF protein) from Escherichia coli B/r. In the present paper we give the experimental evidence for this sequence. Two tryptophan positions, one valine position, two aspartic acid positions and nine out of 82 amide determinations have been corrected. To aid further studies on this class of transmembrane proteins, the isolation of most of the constituent peptides is documented.

Amides↗
PubMed1982

Complete amino acid sequence and glycosylation sites of glycoprotein gp71A of Friend murine leukemia virus.

The complete amino acid sequence of glycoprotein gp71A of Friend murine leukemia virus (F-MuLV) is presented. The protein moiety of gp71A was digested with Staphylococcus aureus (SV8) protease, trypsin, and thermolysin. The sequences of the peptides were determined by the micro dansyl Edman procedure. gp71A is composed of 445 amino acid residues and contains eight oligosaccharide side chains, which are attached exclusively to asparagine by N-glycosyl bonds primarily in the COOH-terminal half of the polypeptide. gp71A is rich in proline (49 residues), tryptophan (16 residues), and cysteine (19 residues). Proline has the highest molar content (11%) of all amino acids. The prolines cluster in two segments. The most interesting one stretches between residue 233 and residue 283 and contains 18 prolines within 51 amino acids. This proline-rich domain most likely forms a flexible polyproline helix. The comparison of gp70 of Moloney murine leukemia virus (Mo-MuLV gp70) with F-MuLV gp71A revealed that 70 amino acids have been exchanged and 9 residues have been deleted from Mo-MuLV gp70. The most striking alterations have taken place within the large polyproline segment (residues 247 to 281). In this part of the molecule 7 amino acids have been deleted in Mo-MuLV and 18 residues have been replaced. This evidence supports the proposal of Shinnick et al. [Shinnick, T. M., Lerner, R. A. & Sutcliffe, J. G. (1981) Nature (London) 293, 543-548] that this area is a "hot spot" for recombination.

Amino Acid Sequence↗
PubMed1982

Early degeneration of porcine xenograft valves in pediatric patients who have undergone apico-aortic bypass.

The glutaraldehyde-preserved stented porcine xenograft valve has been durable in adult patients with a low incidence of valve-related complications. In children, however, early degeneration and calcification of this valve is now being reported. The etiology of the early degeneration is still unclear but may be related to calcium metabolism, tissue fatigue, and host rejection. During the last 5 years at the Texas Heart Institute, 21 patients under 23 years of age underwent implantation of an apico-aortic conduit containing a porcine xenograft valve for treatment of severe forms of left ventricular outflow tract obstruction. Because of early failure, the valve was replaced in two patients (11.5%) within 3 years of implantation. Although early degeneration of the porcine valve might occur in some children, it may still be the preferred valve to use in young patients because anticoagulation is not required with its use.

Journal Article↗
PubMed1981

High-resolution phosphorus nuclear magnetic resonance spectra of yeast phenylalanine transfer ribonucleic acid. Metal ion effects and tentative partial assignment of signals.

The temperature and metal ion dependence of the 31P NMR spectra of yeast phenylalanine tRNA is presented, and a tentative assignment of some of the individual phosphate signals is offered. Signals A, C, F, P, and T have been assigned to the magnesium binding site of phosphates by monitoring the magnesium ion dependence in the 31P NMR spectra. In the presence of 10 mM Mg2+, specific paramagnetic line broadening effects are observed for signals A, D, E, and U upon addition of 0.001-0.1 Mn2+ ion per tRNA molecule. Through the combination of the above metal in experiments, X-ray studies, and earlier 1H and 31P NMR studies [particularly the tRNA modification 31P NMR experiments of Salemink et al. [Salemink, P..J.M., Swarthof T., & Hilbers, C.W. (1979) Biochemistry 18, 3477]], an initial assignment of some of these signals is attempted.

Base Sequence↗
PubMed1981

The reaction of beta-propiolactone with derivatives of adenine and with DNA.

The reaction of deoxyadenosine with beta-propiolactone produces two derivatives. One is 1-(2-carboxyethyl)-2'-deoxyadenosine (CEdA) first described by Maté, et al. The proposed structure for the other is 3-(beta-D-2-deoxyribosyl)-7,8-dihydropyrimido-[2,l-i]purine-9-one (dDPP). Spectral characteristics of both compounds are presented. These include u.v. spectra of each in acidic, neutral and alkaline solutions, i.r. spectra, fluorescence spectra, and n.m.r. spectra. The extinction coefficient for CEdA is 12,900 M--1cm--1 at 258 nm and that for dDPP is 12,400 M--1cm--1 at 305 nm. The dDPP can be converted to CEdA by mild acid hydrolysis, and the CEdA can be converted to dDPP by reaction with a carbodiimide derivative. When poly A was reacted with beta-propiolactone, the yield of dDPP in the polymer was 7-9%. When double-stranded DNA was alkylated by [3H]beta-propiolactone at relatively high concentrations and then acid hydrolyzed to separate 1-(2-carboxyethyl)adenine (CEA) and 7-(2-carboxyethyl)guanine (CEG), a CEA to CEG ratio of up to 0.62 was obtained. With relatively low concentrations of [3H]beta-propiolactone, the yield of CEA was low with double-stranded DNA but was 5--6 fold greater with single-stranded DNA.

Adenine↗
PubMed1980

Primary structure of major outer membrane protein II (ompA protein) of Escherichia coli K-12.

The amino acid sequence of major outer membrane protein II (ompA protein) from Escherichia coli K-12 has been determined. The transmembrane polypeptide consists of 325 residues, resulting in a molecular weight of 35,159. The transmembrane part of the protein is located between residues 1 and 177. In this part of the protein a predominantly lipophilic 27-residue segment exists that perhaps spans the membrane in a mostly alpha-helical conformation, or a 19-residue stretch of this segment might traverse the membrane linearly. Inside the outer membrane a sequence -Ala-Pro-Ala-Pro-Ala-Pro-Ala-Pro- exists that, analogous to the -Cys-Pro-Pro-Cys-Pro- sequence in the hinge region of immunoglobulin, could assume the conformation of a polyproline helix. Computer analysis did not reveal a clear overall pattern of internal homology in the protein; besides the -Ala-Pro- repeat, only one local area (two adjacent dodecapeptide segments) shows some repetitiveness. The same analysis did not produce evidence for internal homology in the previously determined sequence of outer membrane protein I (porin) nor was any marked resemblance detected between transmembrane proteins I and II.

Amino Acid Sequence↗
PubMed1980

Establishment of three human liver carcinoma cell lines and some of their biological characteristics in vitro.

Three cell lines derived from liver carcinoma specimens of two male and one female operated patients have been successfully established in vitro and designated by the names of BEL-7402, BEL-7404 and BEL-7405. In the course of the establishment (from the 2nd transfer onwards) studies were made to characterize them. The doubling time of cell population was found to be 20--26 hr. They formed tumor nodules upon heterologous transplantation. They appeared as epithelial-like cells in morphology and showed, in addition to desmosomes, the presence of cytoplasmic tonofibrills which were typical of epithelial cells by electron microscopy. The ultrastructural features were different from normal human liver cells, but similar to clinical hepatoma cells. They had hypotriploid chromosone number with one abnormally long acrocentric chromosome present in all 3 cell lines and additional small acrocentric chromosome and chromosome fragment in BEL-7405 line of cells. AFP were detected intracellularly by the indirect immunofluorescent method. LDH isoenzyme showed a pattern different from that of human adult liver, but similar to those of embryonic liver and clinical hepatoma with the increase of the percentage of LDH-1 (H-type) at the expanse of LDH-5 (M-type), i.e. with a higher H/M ratio. The results suggest the 3 lines of liver carcinoma cells as rapidly growing and not well differentiated epithelial-like malignant cells.

Aged↗
PubMed1979

Evidence for hemiacetal formation between N-acyl-L-phenylalaninals and alpha-chymotrypsin by cross-saturation nuclear magnetic resonance spectroscopy.

N-Acetyl-L-phenylalaninal exists predominantly in its hydrated form in aqueous solution, but the aldehyde and not the hydrate is shown by nuclear magnetic resonance (NMR) spectroscopy to be the effective inhibitor of alpha-chymotrypsin. NMR spectroscopy also indicates that the initial alpha-chymotrypsin-N-acetyl-L-phenylalaninal complex is in equilibrium with a hemiacetal formed between the aldehyde and the active site serine residue. The rate of the latter equilibration is slow on the NMR time scale but the hemiacetal can be detected by cross-saturation NMR spectroscopy. N-Benzoyl-L-phenylalaninal is a more potent inhibitor of alpha-chymotrypsin than the N-acetyl derivative and both the formation of the enzyme-inhibitor complex and the hemiacetal are slow on the NMR time scale, but the hemiacetal in the enzyme can be detected by cross-saturation NMR spectroscopy. The N-acyl-L-phenylalaninals also bind to N-methylhistidinyl-57-alpha-chymotrypsin, but clear evidence for hemiacetal formation was not obtained by cross-saturation NMR spectroscopy either because the hemiacetal was not formed or more probably because the rate of dissociation was slow compared with the rate of relaxation of the hemiacetal proton. The dissociation constant of N-benzoyl-L-phenylalaninal to dehydroalaninyl-195-alpha-chymotrypsin was found to be high relative to the dissociation constant to native alpha-chymotrypsin, supporting the NMR evidence that a hemiacetal with the Ser-195 is formed on association of N-benzoyl-L-phenylalaninal with alpha-chymotrypsin.

Acetals↗
PubMed1979

Primary structure of major outer membrane protein I of Escherichia coli B/r.

The amino acid sequence of the pore-forming outer membrane protein I (porin) from Escherichia coli B/r has been determined. The polypeptide contains 340 amino acid residues resulting in a molecular weight of 37,205. The transmembrane polypeptide has no stretches of nonpolar residues, uninterrupted by charged side chains, longer than 11 amino acid residues. Regarding polarity, the chain can be subdivided into three regions: a distinctly hydrophilic region between residues 1 and 82 (51.2% polarity), a fairly nonpolar region between residues 83 and 194 (33.9% polarity), and a more hydrophilic region up to the COOH terminus (48% polarity). These results are interpreted as evidence against a simple transmembrane structure in which the membrane is spanned by a single contiguous sequence of hydrophobic amino acids, as has been proposed, for example, for glycophorin.

Amino Acid Sequence↗
PubMed1978

Major proteins of the outer cell envelope membrane of Escherichia coli K12: multiple species of protein I differ in primary structure.

Protein I, one of the major outer membrane proteins of E. coli in most K12 strains is represented by two very similar polypeptides Ia and Ib. Sequential mutations (involving selections for phage resistance) can lead to loss of proteins Ia and Ib. Among "revertants" of such Ia-Ib- mutants clones exist that instead of Ia or Ib produce a third species of protein I, polypeptide Ic. Ichihara and Mizushima [J. Biochem. 83, 1095--1100 (1978)] have shown that proteins Ia and Ib exhibit differences in primary structure. Here evidence is presented indicating that protein Ic also is not identical in primary structure with Ia or Ib. Thus, 3 very similar structural genes appear to exist for the protein I species known to date, and that for Ic normally is silent. Introduction of a functional Ic locus into a Ia+ Ib+ strain caused expression of all three proteins with a reduced rate of synthesis of protein Ia.

Bacterial Proteins↗
PubMed1978

Major proteins of the Escherichia coli outer cell envelope membrane. Sequence of the cyanogen bromide fragments of protein I from Escherichia coli B/r.

The sequence of the cyanogen bromide fragments of one of the major outer membrane proteins of E. coli B/r has been established with the aim of elucidating the primary structure of this protein. Separation of all fragments on one molecular sieve column was achieved upon citraconylation of these fragments. Overlapping peptides were obtained by digestion of the protein, or a cyanogen bromide fragment arising from incomplete cleavage, with trypsin or Staphylococcus aureus protease.

Amino Acid Sequence↗
PubMed1977

Influenza immunization: serologic and clinical responses in military units.

Two inactivated influenza-virus vaccines were tested and compared in three army training units in Israel. The serological responses to the vaccines and the side-effects were assessed. The vaccines contained the influenza strains which were prevalent in 1974: A2/Port Chalmers/1/73 and B/Hong Kong/8/73. One of the vaccines also contained A2/England/42/72. Both vaccines caused a more than three-fold rise in geometric mean titers against influenza A strains, and about a twofold rise in geometric mean titers against influenza B/Hong Kong/5/73. Approximately 75%-80% of the vaccinees acquired protective hemagglutination-inhibition antibody titers against influenza A strains, while less than 30% acquired protective titers against B strains. In general, there were no significant differences between the serological responses to the two vaccines. More than 50% of the vaccinees experienced at least one systemic side-effect (50.3% with one vaccine and 61.0% with the other). The average number of side-effects per person was between 1.78 and 2.11. However, these side-effects were generally of short duration and caused minimal disability. On the whole, the two vaccines did not differ significantly with regard to the side-effects they caused.

Antibody Formation↗