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S L Fong

Publications and source records attributed to S L Fong.

67 records · Page 4Linked to original sources
PubMed1982

Vitamin A in human eyes: amount, distribution, and composition.

The amount, distribution, and composition of vitamin A stored in the eyes of 29 postmortem donors was determined by a combination of techniques, including high-pressure liquid chromatography. The vitamin A concentration in the pigment epithelium-choroid (RPE-Ch) was the highest observed for human non-liver tissue and amounted to 7.9 +/- 4.3 nmol/eye (n = 28), or 10.4 +/- 7.1 microgram/gm (n = 27). There was no evidence for significant losses during the interval between death and enucleation or during subsequent storage at 4 degrees C. The vitamin A extracted from the retina was 15.3% of that in the corresponding RPE-Ch. By measuring rhodopsin regeneration in retinal homogenates incubated with 11-cis retinal, we estimated that the amount of vitamin A in the RPE-Ch of fully dark-adapted eyes would represent 2.5 mole equivalents of the retinal rhodopsin, a value similar to that found in the frog. A preponderance of the vitamin A in the eye was esterified (98.3% in the RPE-Ch, 79.3% in the retina) and consisted principally of stearate and palmitate in the ratio of 1:4.8. A small amount of oleate was also detected. The ratio of 11-cis isomer over the all-trans averaged 1.52 +/- 0.48 (n - 11). Variable, usually small proportions of 13-cis retinyl esters were also present. Intact RPE-Ch or isolated RPE cells esterified exogenous all-trans-3H2-retinol to the same fatty acids in roughly the same proportions as in the endogenous stores. The all-trans configuration was mainly retained during uptake and esterification, although some isomerization to 13-cis also occurred. No 11-cis isomer was formed under these conditions.

Choroid↗
PubMed1981

Comparison of cytosol retinol binding proteins from bovine retina, dog liver, and rat liver.

Cytosol retinol binding proteins (CRBP's) have been purified from rat liver, dog liver, and bovine retina. All had identical molecular weights on sodium dodecyl sulfate electrophoresis. They had different RF values on non-sodium dodecyl sulfate gels at pH 8.9. The three CRBP exhibited similar absorption and fluorescence spectra. The absorbance of the ligand was perturbed after binding, the main band shifting bathochromically and exhibiting a lambda(max) at 350 nm compared with 328 nm for free retinol in hexane. Additionally, subsidiary peaks appeared at 335 and 367 nm. Rabbit antiserum against rat liver CRBP cross-reacted with CRBP's from dog liver and bovine retina. The Ouchterlony immunodiffusion technique indicated that these proteins have molecular structures with identical antigenic determinants. All three CRBP's had amino acid composition that were virtually identical, as judged by our own observations and those of other laboratories. The molecular structure of cytosol retinol binding proteins appears to be highly conserved, irrespective of species or tissue of origin.

Amino Acids↗
PubMed1981

High-pressure liquid chromatography of fatty acid esters of retinol isomers. Analysis of retinyl esters stored in the eye.

We have synthesized the all-trans, 13-cis, 11-cis, and 9-cis retinyl esters of some or all of the following fatty acids: caprylic (8:0), capric (10:0), lauric (12:0), myristic (14:0), palmitic (16:0), stearic (18:0), arachidic (20:0), palmitoleic (16:1), oleic (18:1), linoleic (18:2), linolenic (18:3), arachidonic (20:4), and docosahexaenoic (22:6). Mixtures of these compounds were analyzed by high-pressure liquid chromatography on an Altex 100 chromatograph. This approach has enabled us to investigate and identify both the isomeric form and fatty acid basis of the retinyl esters present in rabbit and rat ocular tissues. Dark-adapted rabbits had 11-cis and all-trans retinyl esters, whereas light-adapted albino rats had only the all-trans isomer. The fatty acids utilized for esterification were almost wholly palmitic for the rabbit, whereas both stearic and palmitic were present in the rat esters. Rabbits are similar to frogs in that a large proportion (80%) of their ocular retinyl esters occurred in large, fluorescent oil droplets in the pigment epithelium. These are absent in rats.

Adaptation, Physiological↗
PubMed1979

Different receptors for distribution of peanut and ricin agglutinins between inner and outer segments of rod cells.

Lectins can be used as probes for cell-surface oligosaccharides1-4. These proteins display high specificities for certain haptene sugars, although the details of the sugar linkages and the three-dimensional array of the oligosaccharide may all be involved in determining the affinity of a lectin for its receptor. We have now shown that peanut and ricin agglutinins bind differentially to the surfaces of rod inner and outer segments.

Animals↗
PubMed1977

The amino- and carboxyl-terminal sequence of bovine rhodopsin.

The amino terminus of bovine rhodopsin is blocked and has the sequence x-Met-Asn(CHO)-Gly-Thr-Glu-Gly-Pro-Asn-Phe-Tyr-Val-Pro-Phe-Ser-Asn(CHO)-Lys-Thr-Gly-Val-Val-Arg, where CHO represents sites of carbohydrate attachment. The carboxyl-terminal sequence of rhodopsin is Val-Ser-Lys-Thr-Glu-Thr-Ser-Gln-Val-Ala-Pro-Ala. Upon short-term digestion of rod outer segment (ROS) membranes with thermolysin, opsin (similar to 35,000 daltons) is converted to a membrane-bound fragment O' (similar to 30,500 daltons) and 2 peptides containing 12 amino acids are released from the carboxyl terminus of rhodopsin into the supernatant. Upon long-term digestion of ROS with thermolysin, opsin and O' are replaced by the membrane-bound fragments F1 (similar to 25,000 daltons), and F2 (similar 9,500 daltons). When 32P-ROS are digested, F2 carries the 32P. Both O' and F1 contain the amino-terminal glycopeptide.

Amino Acid Sequence↗
PubMed1977

Preparation of carboxyl-terminal tryptic peptides from proteins by cleavage at arginine.

A method has been developed for selectively preparing the carboxyl-terminal tryptic peptide of proteins by cleavage at arginyl residues. The succinylated protein is digested with trypsin and the peptides produced are maleylated. Maleylated peptides are then submitted to cation-exchange chromatography in urea at low pH and ionic strength. Arginine-containing peptides are retained by the resin. The carboxyl-terminal peptide emerges unretarded and in pure form. This method has been applied to four proteins of known sequence. Yields as high as 88% have been obtained.

Amino Acids↗
PubMedDate not supplied

A linked genetic marker for multiple endocrine neoplasia type 2A on chromosome 10.

Multiple endocrine neoplasia type 2A (MEN2A) is an autosomal dominantly inherited cancer syndrome characterized by medullary carcinoma of the thyroid, phaeochromocytoma and hyperparathyroidism. Almost all gene carriers can be detected by screening tests before the age of 40, but the nature and location of the predisposing gene are unknown. Simpson et al. recently reported preliminary evidence for linkage between the DNA probe p9-12A on chromosome 10 and MEN2A. We now report linkage between the MEN2A locus and the interstitial retinol-binding protein gene, which is located on chromosome 10p11.2-q11.2.

Centromere↗
PubMedDate not supplied

Compliance among adults with cystic fibrosis.

Advances in therapy have largely contributed to the increased life expectancy of patients with cystic fibrosis. Unlike children, adults with cystic fibrosis must take responsibility for their own care. We administered a questionnaire to 23 adult patients (aged 18-39 years) with cystic fibrosis to (1) determine patients' degree of compliance with medications and chest physiotherapy; (2) collect information on their self-assessment of health motivation, disease severity, and benefits of treatment; and (3) identify barriers to receiving medical care. Patients reported better compliance with medications than with chest physiotherapy. Nine percent of the patients missed at least 25 percent of prescribed medication, whereas 47 percent missed at least 25 percent of prescribed physiotherapy. We observed a trend toward better compliance in patients who were highly worried about their health, who believed their illness to be serious, and who felt that their medications were very effective. Less than half of the study participants believed physiotherapy to be effective, and that adhering to a physiotherapy schedule was very difficult. Among adults with cystic fibrosis, compliance can be a serious problem that minimizes the benefits of good medical care. We suggest that emphasizing the severity of disease and usefulness of therapy may improve compliance and requires study.

Adolescent↗