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Biomedical subjects

H Yoo

Publications and source records attributed to H Yoo.

42 records · Page 3Linked to original sources
PubMed1992

Comparison of three tetramic acids and their ability to alter membrane function in cultured skeletal muscle cells and sarcoplasmic reticulum vesicles.

Cyclopiazonic acid is a potent inhibitor of calcium uptake and Ca(2+)-ATPase activity in sarcoplasmic and endoplasmic reticulum. In L6 muscle myoblasts, cyclopiazonic acid stimulates the uptake of tetraphenylphosphonium, a lipophilic membrane potential probe, and has antioxidant properties. The purpose of the present study was to investigate the structural requirements necessary for causing the surface charge alterations, and the antioxidant activity in L6 skeletal muscle myoblasts, and for inhibition of calcium transport by rat skeletal muscle sarcoplasmic reticulum vesicles. This was accomplished by comparing the effects of two structurally related tetramic acids, cyclopiazonic acid imine and tenuazonic acid, with cyclopiazonic acid. Cyclopiazonic acid imine inhibited oxalate-assisted 45Ca2+ uptake and ATPase activity in sarcoplasmic reticulum vesicles and stimulated tetraphenylphosphonium accumulation by L6 muscle myoblasts. However, these effects required an approximately fourfold higher concentration than that of cyclopiazonic acid. Tenuazonic acid, up to 1 mM, had no effect on oxalate-assisted 45Ca2+ uptake or Ca(2+)-ATPase activity in sarcoplasmic reticulum vesicles and did not stimulate tetraphenylphosphonium accumulation by L6 muscle myoblasts. Cyclopiazonic acid was only slightly more effective than cyclopiazonic acid imine at preventing the patulin-induced increase in thiobarbituric acid positive substance (used to estimate lipid peroxidation); tenuazonic acid was totally ineffective. Previously, it was shown that cyclopiazonic acid was twice as effective as cyclopiazonic acid imine at preventing increases in thiobarbituric acid positive substance in cultured renal cells, LLC-PK1. Thus, the indole nucleus of cyclopiazonic acid is essential for the membrane-associated biological activity; however, modification of the acetyl group reduces the potency of the activity.

Animals↗
PubMed1989

In vitro DNA cytosine methylation of cis-regulatory elements modulates c-Ha-ras promoter activity in vivo.

The effect of DNA cytosine methylation on promoter activity was assessed using a transient expression system employing pHrasCAT. This 551 bp Ha-ras-1 gene promoter region is enriched with 84 CpG dinucleotides, six functional GC boxes, and is prototypic of many genes possessing CpG islands in their promoter regions. Bacterial modification enzymes HhaI methyl transferase (MTase) and HpaII MTase, alone or in combination with a human placental DNA methyltransferase (HP MTase) that methylates CpG sites in a generalized manner, including asymmetric elements such as GC box CpG's, were used to methylate at different types of sites in the promoter. Methylation of HhaI and HpaII sites reduced CAT expression by approximately 70%-80%, whereas methylation at generalized CpG sites with HP MTase inactivated the promoter by greater than 95%. The inhibition of H-ras promoter activity was not attributable to methylation-induced differences in DNA uptake or stability in the cell, topological form of the plasmid, or methylation effects in non-promoter regions.

Animals↗
PubMed1987

Pig brain aldose reductase: purification, significance of the amino acid composition, substrate specificity and mechanism.

1. Pig brain aldose reductase (ALR2, EC 1.1.1.21) has been purified from fresh tissue with a approximately 60% improvement in specific activity over an acetone-powder preparation. 2. Dead-end inhibition and alternate substrate studies rule out an iso Theorell-Chance mechanism but are compatible with an ordered bi bi mechanism where NADPH and NADP+ function as the outside reactants in the direction of xylitol formation. 3. Subtle but significant differences are shown to exist in the distribution of apolar and mixed amino acid residues between aldose and aldehyde reductases when the mean fractional area loss [Rose et al., 1985] is used as the measure of compositional relatedness.

Aldehyde Reductase↗
PubMedDate not supplied

Actinomycin D binding to unstructured, single-stranded DNA.

Actinomycin D is an anticancer antibiotic best know for inhibiting transcription by binding double-stranded DNA. Tight, sequence selective binding of actinomycin to single-stranded DNA is also known, however, and is implicated in biological activities including inhibition of (-) strand transfer by HIV reverse transcriptase. Oligonucleotide d(GTTAACCATAG) is one of the rare single-stranded DNAs that lack GC steps yet have high affinity for actinomycin. Oligonucleotide sequence and length requirements for drug binding were investigated by monitoring association of the fluorescent surrogate, 7-aminoactinomycin D, to d(GTTAACCATAG) and 31 related oligomers. The TAG-3' terminal sequence was essential for high-affinity binding, but was not sufficient. Five oligomers with TAG sequences on or near the 3'-end had high affinity [K(d) < or = 200 nM (oligomer)]. A sixth oligomer, d(GTAACCATATG), had moderately lower affinity (Kd = 370 nM), and other homologous oligomers had much lower affinity. The minimum length sequence for tight binding of 7-aminoactinomycin D was identified as only eight nucleotides, corresponding to d(AACCATAG). This octanucleotide is unstructured in the absence of actinomycin, and has the highest drug affinity of all oligomers examined (Kd = 125 nM). These studies show that high-affinity binding of 7-aminoactinomycin, and actinomycin D by extension, to single-stranded DNA does not require pre-existing secondary structure or any apparent propensity for secondary structure. It is proposed that actinomycin D binds to certain single-stranded DNA sequences by an induced-fit mechanism favored by participation of at least eight nucleotides, or the equivalent of four base pairs.

Base Sequence↗
PubMedDate not supplied

Langerhans' cell histiocytosis as a cause of periportal abnormal signal intensity on MRI.

Three cases of hepatic Langerhans' cell histiocytosis (LCH) manifesting as periportal abnormal signal intensity on magnetic resonance images are described. One case also demonstrated intrahepatic bile duct dilatation due to secondary sclerosing cholangitis. Hepatic involvement of LCH could be included in the differential diagnosis of periportal abnormal signal intensity in children.

Histiocytosis, Langerhans-Cell↗