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Biomedical subjects

C C Yip

Publications and source records attributed to C C Yip.

At least 91 records · Page 5Linked to original sources
PubMed1973

Insulin biosynthesis in the bullhead, Ictalurus nebulosus, and the effect of temperature.

Insulin biosynthesis in the brown bullhead, Ictalurus nebulosus (Le Sueur), was studied by measuring the incorporation in vitro of [(3)H]leucine into proteins of the principal islet. The tissue was incubated for 6-15h in Krebs-Ringer bicarbonate buffer with [(3)H]leucine, supplemented with amino acids and glucose. Proteins, precipitated with trichloroacetic acid and extracted with acid ethanol, were separated by gel-filtration on Biogel P-30 in 3m-acetic acid. Three major components were found after incubation of the islets at 22 degrees C. On the basis of the results of sulphitolysis, biological activity and the demonstrated precursor-product relationship, components I and II were identified as proinsulin and insulin respectively. The third component was not identified. At 12 degrees C, [(3)H]leucine was incorporated only into proinsulin. No radioactivity was found in insulin or the unidentified component III at 12 degrees C as was found after incubation at 22 degrees C. When the temperature was lowered from 22 degrees to 12 degrees C after 3h of a 15h incubation, decreased conversion of proinsulin into insulin resulted at the lower temperature compared with the control tissue maintained at 22 degrees C. When the temperature was raised from 12 degrees to 22 degrees C at 3h of a 15h incubation, conversion of proinsulin into insulin occurred. No conversion occurred in the control tissue with the temperature maintained at 12 degrees C. No qualitative difference in the incorporation of [(3)H]leucine into proinsulin and its conversion into insulin at 12 degrees and 22 degrees C could be demonstrated between islet tissue from fish acclimated to less than 12 degrees C or to 22 degrees C. The results suggest that the enzyme(s) responsible for converting proinsulin into insulin in the bullhead may be temperature sensitive with low activity at 12 degrees C.

Amino Acids↗
PubMed1971

A bovine pancreatic enzyme catalyzing the conversion of proinsulin to insulin.

An enzyme that catalyzes the conversion of bovine proinsulin to insulin has been purified from a bovine pancreatic extract. The product of conversion was identified as insulin by aminoacid analysis and determination of carboxyl terminal aminoacid residues. The purified enzyme preparation showed one major protein band on polyacrylamide gel disc electrophoresis; it had a molecular weight of about 70,000 and an isoelectric point (pI) at a pH of 4.82.

Amino Acids↗
PubMed1969

A specific anti-proinsulin serum and the presence of proinsulin in calf serum.

A specific antibody against proinsulin has been obtained by adsorbing the original anti-proinsulin guinea pig serum with a solid immunosorbent of Sephadex-insulin. The specificity of the antibody against antigenic determinants of proinsulin was established by radioimmunoassay and by passive cutaneous anaphylaxis (PCA) tests. The presence of proinsulin in calf serum has been demonstrated by (a) gel filtration of an acid alcohol extract of the serum followed by immunoassays of the fractions using anti-insulin or the specific anti-proinsulin serum, and (b) direct assay of calf serum with the specific anti-proinsulin serum.

Animals↗
PubMed1969

Biosynthesis of insulin in bovine fetal pancreatic slices: the incorporation of tritiated leucine into a single-chain proinsulin, a double-chain intermediate, and insulin in subcellular fractions.

This communication reports the biosynthesis of insulin in the bovine fetal pancreatic slices in vitro. Double-chain proinsulin and insulin were found as major components in the mitochondrial-granule fraction of bovine fetal pancreas. Tritiated leucine was incorporated into a single-chain proinsulin, a double-chain proinsulin, and insulin. Subcellular fractionation of the slices incubated with tritiated leucine showed that radioactive single-chain proinsulin was present in the deoxycholate-soluble microsomal fraction, deoxycholate-insoluble microsomal fraction, and mitochondrial-granule fraction. Labeled double-chain proinsulin and insulin were present in the deoxycholate-soluble microsomal and mitochondrial-granule fractions. These results are consistent with the hypothesis that insulin is synthesized as a single-chain polypeptide on the ribosomes, and that intracellular proteolysis in the subcellular membranous organelles and beta-granules converts the single-chain proinsulin to insulin via a double-chain intermediate.

Animals↗
PubMedDate not supplied

Preparation of N epsilon B28-monoazidobenzoyl insulin-like growth factor I and photoaffinity labeling of insulin-like growth factor I receptor.

Recombinant human insulin-like growth factor I (hIGF-I) was reacted with azidobenzoyl hydroxysuccinimide to produce a mixture of photoactive hIGF-I derivatives. The mixture was purified by reversed-phase HPLC to yield three mono-substituted azidobenzoyl hIGF-Is. One of the derivatives was identified by amino acid sequencing as N epsilon B28-monoazidobenzoyl hIGF-I. This derivative was indistinguishable from native hIGF-I when bioassayed in Rat-1 fibroblasts. A 120-kDa band, the alpha subunit of the IGF-I receptor, was specifically labeled in Rat-1 plasma membranes by this photoprobe. The labeling of this band was reduced by hIGF-I at 1 nM and completely abolished by hIGF-I, but not insulin, at 100 nM, indicating the specificity of the photolabeling of the IGF-I receptor by this fully active IGF-I photoprobe.

Affinity Labels↗
PubMedDate not supplied

Outcome of late probing for congenital nasolacrimal duct obstruction in Singapore children.

OBJECTIVE: To evaluate the outcome of late probing in a mixed Asian children population with congenital nasolacrimal duct obstruction (CNLDO) and whether probing was associated with an increased risk of infection. METHOD: A retrospective clinical study was conducted. A clinical diagnosis of CNLDO was defined in an infant who presented with a history of tearing and/or eye discharge up to 1 year of age with no other accompanying ocular pathology. All patients with a presumed diagnosis of CNLDO who had probing after 12 months of age were included in our study. Prior to probing, most patients had a trial of conservative treatment with massage and/or topical antibiotics. Intra-operative patency of probing was determined when metal to metal contact of the probe and forceps was achieved and/or when fluorescein dye was recovered from the nose after syringing. Successful probing was defined as a resolution of symptoms within 1 month after probing. RESULTS: Seventeen patients involving 19 eyes fulfilled our inclusion criteria for this study. Fourteen (82%) infants were Chinese, two Malays (12%) and the remaining one Indian (6%). There were 10 males (59%) and 7 females (41%) and the mean age at probing was 2.2 years (range, 14 months to 5 years 6 months). The subjects were followed-up post-operatively for a mean duration of 21.2 months (range, 2 months to 8 years). Successful probing in our series was 89.5% (17/19 eyes). Of the two eyes with persistent tearing, one resolved with massage about 9 months after the unsuccessful probing; the other was referred to the oculoplastic service for further management. CONCLUSION: Late probing after 13 months old appears to be an effective approach in the management of CNLDO in Asian infants.

Child, Preschool↗
PubMedDate not supplied

Low-dose intravenous methylprednisolone or conservative treatment in the management of traumatic optic neuropathy.

PURPOSE: To compare the efficacy of low-dose intravenous methylprednisolone or conservative treatment in the management of traumatic optic neuropathy. METHODS: A non-randomized retrospective study of 21 patients (21 eyes) with traumatic optic neuropathy treated between October 95 and November 97 in a tertiary ophthalmology unit. Traumatic optic neuropathy was defined as traumatic visual loss with afferent pupillary defect in the absence of direct injury to the globe or optic nerve. The median follow-up period was one year. Nine patients were treated with 125-250 mg methylprednisolone 6-hourly intravenously for a mean of 3.3 days (range 2-5 days) and 12 patients were treated conservatively. Visual acuity (VA) was measured with a Snellen chart before and after treatment at each follow-up visit. Visual recovery was defined as an improvement of 2 or more Snellen lines one week post-injury or later. RESULTS: The patients' mean age was 37.1 years (range 12-65 years). There were more males (90.5%) than females (9.5%). Traumatic optic neuropathy was in 12 right eyes and 9 left eyes. The cause of injury included traffic accidents (52.4%), falls (28.6%), assault (14.2%) and others (4.8%). The mean interval between the injury and steroid therapy was 3.6 days (range 1-11 days). Visual recovery was observed in 44.4% of eyes treated with methylprednisolone and in 33.3% treated conservatively (p = 0.673, Fisher's exact test). CONCLUSIONS: Intravenous methylprednisolone at the dosage and duration used in this retrospective study did not significantly improve the visual recovery of eyes with traumatic optic neuropathy compared to conservative treatment. However, this small sample may not be sensitive enough to detect a small difference in visual recovery rates, and further studies with larger samples may be warranted.

Adolescent↗