PubMed Health⌕ Search

Biomedical subjects

C J Sih

Publications and source records attributed to C J Sih.

At least 19 recordsLinked to original sources
PubMed2001

Difference in susceptibility of tyrosine residue to oxidative lodination between a thioredoxin box region and a hormonogenic region.

Peptide fragments, isolated from proteolytic cleavage of thyroglobulin at specific sites, were examined for the iodination of tyrosine residues. The 50 kDa polypeptide, which was prepared from digestion of bovine thyroglobulin and continuous preparative SDS-PAGE, was subjected to reduction with DTT and alkylation with iodoacetic acid to generate S-carboxymethylated peptide derivative, which was further hydrolysed by endoproteinase-Asp N. Peptide products were separated by RP-HPLC, and each fraction was analyzed by LC/ ESI-MS and MALDI-MS analyses. Based on the specificity of endoproteinase Asp-N and the mass spectra data, a peptide fragment turned out to correspond to a peptide, DALGCVKCPEGSYFQ (1438-1452), characterized by the presence of a thioredoxin box (CVKC) and a tyrosine residue. In addition, another peptide fragment (1453-1465) containing a thioredoxin box (CIPC) and a tyrosine residue was also observed. However, any evidence of iodination of the tyrosine residue present in these peptides was not provided. Meanwhile, tyrosine residues in the peptides, DVEEALAGKYLAGRFA (1366-1381) and DYSGLLLAFQVFLL (1290-1303) were found to be iodinated; mono- or diiodinated tyrosine residues, characteristic of a hormogenic site, existed in both peptides. In addition, the tyrosine residue in the peptide (1218-1252), corresponding to a hormonogenic site was also iodinated. Thus, there was a sharp difference of the susceptibility to oxidative iodination between the tyrosine residue in a hormonogenic site and that in a thioredoxin region. From these results, it is suggested that polypeptide region adjacent to tyrosine residues may govern the susceptibility of tyrosine to oxidative iodination.

Amino Acid Sequence↗
PubMed2000

Inhibition of hepatic stearoyl-CoA desaturase activity by trans-10, cis-12 conjugated linoleic acid and its derivatives.

Conjugated linoleic acid (CLA) has been reported to decrease stearoyl-CoA desaturase (SCD) activity by decreasing mRNA expression. This investigation was designed to determine whether structurally related compounds of CLA have a direct inhibitory effect on SCD activity. Trans-10,cis-12 CLA had strong inhibitory activity on SCD while cis-9,trans-11, and trans-9,trans-11 isomers had no effect. Trans-10 octadecenoate was not inhibitory, whereas cis-12 octadecenate was inhibitory, but not as effective as trans-10,cis-12 CLA. Of the oxygenated derivatives, 9-peroxy-cis/trans-10, trans-12 octadecadienoate was a more effective inhibitor than trans-10,cis-12 CLA, whereas 9-hydroxy-trans-10, cis-12 octadecadienoate was less effective. Interestingly, cis-11 octadecadienoate and cis-12 octadecen-10-ynoate were slightly inhibitory. However, trans-9 and trans-11 octadecenoates, and trans-9,cis-12 octadecadienoate were all inactive under test condition, as were linoleate, oleate, and arachidonate. Derivatives of CLA acid modified to alcohol, amide or chloride were all inactive. A cis-12 double bond appears to be a key structural feature for inhibiting SCD activity, especially when coupled with a trans-10 double, whereas a cis-11 double bond is less effective.

Animals↗
PubMed1999

Synthesis of 9Z,11E-octadecadienoic and 10E,12Z-octadecadienoic acids, the major components of conjugated linoleic acid.

Linoleic acid was efficiently converted into the two major components of conjugated linoleic acid, 9Z,11E-octadecadienoic (1a) and 10E,12Z-octadecadienoic acid (1b) using either the superbase (n-butyllithium/potassium tert-butoxide) or by simply refluxing with KOH in 1-butanol. In turn, 1a and 1b were separated from each other using the lipase from Aspergillus niger via stereoselective esterification in 1-butanol. This enzyme has a preference for the 9Z,11E isomer, 1a, and has excellent selectivity. This method has allowed the ready preparation of gram quantities of 1a and 1b in their highly purified forms, which are not readily accessible by current methods.

Animals↗
PubMed1999

Bioorganic chemistry of cyclic ADP-ribose (cADPR).

The objective of this brief review is to present an overview of the bioorganic chemistry of cyclic-ADP-ribose (cADPR) with special emphasis on the methodology used for the synthesis of analogues of cADPR. New structural analogues of cADPR can be prepared using either the biomimetic method or ADP-ribosyl cyclase from Aplysia californica. For the most part, both procedures give similar product profiles, but higher yields are generally obtained with the enzymatic method. These synthetic methodologies have allowed the transformation of a variety of structurally modified analogues of NAD+ into their corresponding cyclic nucleotides. Several of these novel analogues are more potent than cADPR in inducing calcium release and are also more stable towards degradative enzymes. They could serve as valuable affinity probes for the isolation of cADPR-binding proteins.

ADP-ribosyl Cyclase↗
PubMed1995

Isolation and identification of C-terminal peptides of proteins.

A method for the isolation and identification of C-terminal peptides of proteins has been developed. The procedure entails the racemization of the C-terminal amino acid by reaction of the N-trifluoroacetylated protein with acetic anhydride and pyridine. After deprotection, the protein is fragmented to yield a mixture of peptides, which in turn are digested with carboxypeptidases. All peptides are hydrolyzed to L-amino acids except the C-terminal peptide with the terminal D-amino-acid residue. It is resistant to the action of carboxypeptidases and is readily identified by peptide mapping.

Acetic Anhydrides↗
PubMed1994

L-carnitine via enzyme-catalyzed oxidative kinetic resolution.

L-Carnitine of high optical purity was prepared via kinetic resolution using a mutant strain of Acinetobacter calcoaceticus ATCC 39647. This organism preferentially metabolized the D-enantiomer of the racemate to furnish L-carnitine. Recovery of L-carnitine was 93%, providing a total weight yield of 46.5% in 92% enantiomeric excess. The mode of degradation of carnitine was shown to proceed via a monooxygenase-catalyzed oxidative cleavage resulting in the formation of trimethylamine and malic acid. The data suggest that the stereoselective metabolism of DL-carnitine is probably the result of differential permeability of the cell membrane towards the optical antipodes.

Acinetobacter calcoaceticus↗
PubMed1985

Extending the applicability of esterases of low enantioselectivity in asymmetric synthesis.

A strategy for expanding the applicability of esterases of low enantioselectivity for asymmetric synthesis is described. This concept is generally applicable to biochemical processes involving enantiotopic group differentiation. Quantitative expressions have been derived to permit the prediction of enantiomeric excess and the optimization of optical and chemical yields.

Chemical Phenomena↗
PubMed1983

Mechanisms of leukotriene formation: hemoglobin-catalyzed transformation of 15-HPETE into 8,15-DiHETE and 14,15-DiHETE isomers.

Four isomers of 8,15-diHETE as well as 14,15-diHETEs are isolated and characterized after exposure of 15-HPETE to hemoglobin. It is found that 83% of the C-8 oxygen atoms in 8(R), 15(S)-diHETE and 8(S), 15(S)-diHETE, and 41% of the C-8 oxygen atoms in 8(R), 15(S)-11Z-diHETE and 8(S), 15(S)-11Z-diHETE are derived from H2(18)O. These results suggest that hemoglobin catalyzes the transformation of 15-HPETE into these products via a free radical process, possibly involving the intermediacy of 14,15-LTA. Intact human leukocytes contain a distinct enzyme system for catalyzing the conversion of 15-HPETE into 14,15-LTA. This enzyme activity is inhibited by ETYA and is rapidly denatured upon homogenization of the intact leukocytes.

Animals↗
PubMed1981

Formation of 11-trans slow reacting substances.

Under strongly basic conditions [excess LiOH, dimethoxyethane/water (4:1, vol/vol)], purified slow reacting substances (SRSs) SRS-GSH and SRS-Cys were not isomerized to their corresponding 11-trans isomers. However, addition of thiols such as glutathione (GSH) or L-cysteine to this basic medium produced various amounts of 11-trans-SRS, depending on the thiol concentration. This chemical isomerization was inhibited by the radical scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidinooxy free radical (HTMP); the inhibition suggests that the thiyl radical (RS) is added reversibly to the triene system at C-12, resulting in the overall cis leads to trans isomerization of the 11,12 double bond. Because the amount of 11-trans-SRS-Cys produced by intact rat basophilic leukemia (RBL-1) cells was consistently higher than the amount produced in boiled cells, we believe that intact RBL-1 cells contain enzyme systems that form peroxides, which are known to enhance the formation of thiyl radicals, required for cis leads to trans isomerization. Likewise, HTMP inhibited the formation of 11-trans-SRS-Cys in this cell system.

Animals↗
PubMed1980

Synthesis of [5,6-3H]arachidonic acid and its use in development of a sensitive assay for prostacyclin synthetase.

[5,6-3H]arachidonic acid has been prepared by catalytic reduction of eicosa-cis-8,11,14-trien-5-ynoic acid (IV) over Lindlar catalyst. When either [5,6-3H]arachidonic acid or [5,6-3H]PGH2 is converted into PGI2 by swine aortic microsomes, the tritium at C-6 is lost to the medium. Thus, the progress of this enzymic rearrangement may be monitored by following the rate of tritium release. As swine aortic microsomes contain only low levels of cyclooxygenase, it is necessary to fortify the system with ram seminal vesicular microsomes (rich in cyclooxygenase) when [5,6-3H]arachidonic acid is used as the indirect substrate.

8,11,14-Eicosatrienoic Acid↗
PubMed1980

Identification of the slow reacting substances from cat paws.

Perfusion of cat paws with compound 48/80 released two slow reacting substances (SRSs) which were isolated and characterized as 5-hydroxy-6-S-cysteinylglycyl-7,9,11,14-icosatetraenoic acid (SRS I) and 5-hydroxy-6-S-cysteinyl-7,9,11,14-icosatetraeonic acid (SRS II) on the basis of chemical degradations, amino acid analyses, spectroscopic and enzymic experiments, and comparison with synthetic samples. The smooth muscle-contractile activities of synthetic 5-hydroxy-6-gamma-glutamylcysteinylglycyl-7,9,11,14-icosatetraenoic acid, synthetic 5-hydroxy-6-S-cysteinyl-7,9,11,14-icosatetraenoic acid, and SRS II were not inactivated by arylsulfatase. On the other hand, the spasmogenic activities produced by synthetic 5-hydroxy-6-S-cysteinylglycyl-7,9,11,14-icosatetraenoic acid and SRS I were destroyed at the same rate by the arylsulfatase. This mode of inactivation was attributed to an aminopeptidase activity in the arylsulfatase preparation because 5-hydroxyl-6-S-cysteinyl-7,9,11,14-icosatetraenoic acid was isolated and identified as the reaction end product. Because the properties of SRS from cat paws closely resemble those of SRS generated by immunological stimulation of human tissues (SRS-A) and because all known SRS-A are inactivated by arylsulfatases, we contend that 5-hydroxy-6-S-cysteinylglycyl-7,9,11-14-icosatetraenoic acid (SRS I) corresponds to SRS-A.

Amino Acids↗
PubMed1980

Characterization of slow reacting substances (SRSs) of rat basophilic leukemia (RBL-1) cells: effect of cysteine on SRS profile.

When RBL-1 cells were incubated with L-cysteine (7.5 mM) and the ionophore A23187, the slow reacting substances SRS-GSH and SRS-Cys-Gly were formed. When L-cysteine was omitted in the incubation, SRS-GSH and SRS-Cys were isolated but only a trace amount of SRS-Cys-Gly was detectable. Each of the characterized SRSs was accompanied by an as yet uncharacterized structural isomer showing UV absorption at 278 nm. L-Cysteine and other thiols inhibited an aminopeptidase that transforms the highly bioactive SRS of anaphylaxis (SRS-Cys-Gly) into the less bioactive SRS-Cys. SRS-GSH, SRS-Cys-Gly, and SRS-Cys may be readily distinguished from each other by means of their bioactivities, antagonism by FPL 55712, and relative susceptibilities to the actions of soybean lipoxygenase, microsome-bound leucine aminopeptidase, and gamma-glutamyl transpeptidase.

Amino Acid Sequence↗