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H Y Chang

Publications and source records attributed to H Y Chang.

At least 145 records · Page 8Linked to original sources
PubMed1990

Paraquat-resistant cell lines derived from Chinese hamster ovary cells.

Two paraquat-resistant clones, PR-1 and PR-2, were selected from CHO K1 cells pretreated with ethyl methanesulfonate. PR-1 and PR-2, routinely cultured in a normal medium without paraquat, were six fold more resistant to paraquat than the parental CHO K1 cells. There was no difference in the uptake of [3H]paraquat among PR-1, PR-2, and CHO K1 cells. Both PR-1 and PR-2 cells showed no cross resistance to free radical generating agents and no increase in total activity of superoxide dismutase. The activities of paraquat-dependent NADPH oxidase and glucose-6-phosphate dehydrogenase were significantly reduced in PR-1 and PR-2 cells, hence the rate of paraquat radical formation will be limited. In addition, an elevation of glutathione levels in PR-1 cells or an increase in glutathione S-transferase activity in PR-2 cells may also play a certain role in protective mechanisms against the toxicity of paraquat.

Animals↗
PubMed1990

The acylation of 1-acyl-sn-glycero-3-phosphate by neuronal nuclei and microsomal fractions of immature rabbit cerebral cortex.

The acylation of 1-acyl-sn-glycero-3-phosphate to form phosphatidic acid was studied using a neuronal nuclear fraction N1 and microsomal fractions P3, R (rough), S (smooth), and P (neuronal microsomes from nerve cell bodies) isolated from cerebral cortices of 15-day-old rabbits. The assays contained this lysophospholipid, ATP, CoA, MgCl2, NaF, dithiothreitol, and radioactive palmitate, oleate, or arachidonate. Of the subfractions, N1 and R had the highest specific activities (expressed per micromole phospholipid in the fraction). The rates with oleate were two to four times the values seen for phosphatidic acid formation from sn-[3H]glycero-3-phosphate and oleoyl-CoA. Using oleate or palmitate, fraction R had superior specific rates to N1 at low lysophosphatidic acid concentrations. With increasing lysophospholipid concentrations the specific rates of N1 and R came closer together and maintained at least a twofold superiority over fraction P. Fraction S had the lowest specific rates of phosphatidic acid formation. Fractions N1, R, and P showed a preference for palmitate and oleate over arachidonate, particularly at low concentrations of lysophosphatidic acid. For N1 and R, the preference was also more marked at higher concentrations of fatty acid. Thus a selectivity for saturated and monounsaturated fatty acids was shown in the formation of phosphatidic acid, as was a concentration of acylating activity in the neuronal nucleus and the rough endoplasmic reticulum.

Acylation↗
PubMed1989

Mitochondrial DNA evolution in the Drosophila nasuta subgroup of species.

The Drosophila nasuta group consists of about 12 closely related species distributed throughout the Indo-Pacific region. They are of great interest because of their evolutionary idiosyncrasies including little morphological differentiation, the ability to intercross in the laboratory often producing fertile offspring, and substantial chromosomal evolution. Studies of metric traits, reproductive isolation, and chromosomal and enzyme polymorphisms have failed to resolve the phylogeny of the species. We report the results of a survey of the mitochondrial DNA (mtDNA) restriction patterns of the species. The phylogeny obtained is consistent with other available information and suggests that D. albomicans may represent the ancestral lineage of the group. The amount of polymorphism in local populations (pi = 1.0% per site) is within the typical range observed in other animals, including Drosophila. The degree of differentiation between species is, however, low: the origin of the group is tentatively dated about 6-8 million years ago. This study confirms the usefulness of mtDNA restriction patterns for ascertaining the phylogeny of closely related species.

Animals↗
PubMed1988

The formation of phosphatidic acid de novo: a comparison of activities in neuronal nuclei and microsomes isolated from immature rabbit cerebral cortex.

The formation of phosphatidic acid from sn-glycerol 3-phosphate was studied in neuronal nuclear fraction N1 and a microsomal fraction P3, isolated from cerebral cortices of 15-day-old rabbits. Two assays were used, employing dithiothreitol, MgCl2, NaF and (A) sn-glycerol 3-phosphate, [14C]oleate, ATP and CoA or (B) sn-[3H]glycerol 3-phosphate and oleoyl-CoA. In both assays fraction N1 had specific rates of phosphatidic acid labelling (expressed per mumol phospholipid in the fraction) which were 5- to 6-times the corresponding values for P3. In contrast to N1, the formation of phosphatidic acid by fraction P3 was more sensitive to inhibition at high concentrations of oleoyl-CoA and was greatly dependent upon the presence of NaF. In the absence of this salt, P3 showed decreased phosphatidate formation and increased levels of radioactive monoacylglycerols. Using cerebral cortex, rough (R) and smooth (S) microsomal fractions were prepared, as was a microsomal fraction P from isolated nerve cell bodies. P had specific rates of phosphatidic acid labelling which were 2-3 times the values for P3, but were about 50% of the N1 values. This indicates a concentration of phosphatidate synthesis in the nucleus within the nerve cell. Specific rates for fraction R were higher and were similar to those of N1. In S, P3 and R the specific rates of phosphatidic acid synthesis paralleled specific RNA contents and indicated a location for phosphatidic acid synthesis within the rough endoplasmic reticulum.

Animals↗
PubMed1987

The incorporation of fatty acids into triacylglycerols of isolated neuronal nuclear envelopes: the influence of thiol reducing reagents and chromatin.

Using [3H]arachidonate, ATP, coenzyme A, MgCl2, EGTA and CMP, triacylglycerols were labelled in an isolated neuronal nuclear fraction, N1 (from immature rabbit cerebral cortex). When the radioactive nuclear fraction N1 was subfractionated, 75% of the labelled triacylglycerol product was located in the nuclear envelope fraction, E, indicating that the fatty acid incorporation was taking place at the nuclear membrane. However, when nuclear envelope fraction E was first isolated and then incubated with radioactive fatty acid, a significant incorporation into triacylglycerol was found only when nuclear envelope fractions had been prepared in the presence of dithiothreitol or mercaptoethanol. The use of the thiol compounds during the isolation of nuclear envelope fraction E led to specific incorporation rates (based on phospholipid content) which were at best 45-56% of the corresponding values seen for the parent nuclear N1 fraction. This was seen for nuclear envelope fractions isolated by two different procedures. Specific rates for acyl-CoA synthetase and diacylglycerol generation (by cholinephosphotransferase) were measured in nuclear envelope fractions and found to be similar to specific rates for these enzymes in the nuclear N1 fraction. The deficiency in triacylglycerol labelling in nuclear envelope fractions was likely due to impaired diacylglycerol acyltransferase activity. Higher specific rates of triacylglycerol labelling (82-90% of N1 values) were seen in nuclear envelope fractions assayed very shortly after preparation and in another subfraction of nuclear fraction N1 which contained small amounts of phospholipid and high concentrations of nucleates and protein. These data suggest that triacylglycerol formation may be maintained by the presence of chromatin, while in its absence there is a loss of acylation activity in nuclear envelope fractions.

Animals↗
PubMed1987

Mouse N-ras genes: organization of the functional locus and of a truncated cDNA-like pseudogene.

The N-ras gene was first identified in both humans and mice as a mutationally activated oncogene found in tumors. The nucleotide sequence and intron/exon structure of the coding region of the mouse gene have been determined previously. We have now determined the sequence and intron/exon structure of the 5' and 3' untranslated regions of mouse N-ras. Like its human homolog, the 3' untranslated region of the gene is encoded by two exons, and the 5' region is encoded by one. In addition, we have isolated and sequenced a second mouse gene homologous to N-ras. This locus, which we have named N-ras-2ps, resides at a chromosomal site distinct from N-ras and appears to be a truncated cDNA-like pseudogene.

Animals↗
PubMed1986

A comparison of the acylation of 1-acyl-sn-glycero-3-phosphoinositol and 1-acyl-sn-glycero-3-phosphocholine in neuronal nuclei in vitro using radioactive arachidonate and oleate.

A neuronal nuclear fraction (N1) was isolated from cerebral cortices of 15-day-old rabbits. Samples of N1 were incubated with a radioactive fatty acid ([3H]arachidonate or [14C]oleate), acylation cofactors, and 1-acyl-sn-glycero-3-phosphoinositol (1-acyl-GPI) or 1-acyl-sn-glycero-3-phosphocholine (1-acyl-GPC). In competition studies, both radioactive fatty acids were incubated with one lysophospholipid or the two lysophospholipids were incubated with one radioactive fatty acid. Using [3H] arachidonate and one lysophosphoglyceride, a maximal rate of incorporation into phosphatidylinositol (PI) was found at a relatively low concentration of 1-acyl-GPI (10 microM), while increasing rates of incorporation into phosphatidylcholine (PC) were seen with increasing concentrations of 1-acyl-GPC (to 65 microM). At low concentrations of lysophosphoglyceride (less than or equal to 25 microM) the rate of arachidonate incorporation into PI greatly exceeded rates of arachidonate incorporation into PC. This higher rate of arachidonate incorporation into PI was also seen in incubations where both lysophospholipids were present. For oleate, greater rates of incorporation into PC were found in comparison with rates of labelling of PI in assays using relatively high concentrations of one or both lysophospholipids. When comparing arachidonate and oleate, in assays with one or both fatty acids, the polyunsaturate showed at least threefold higher rates of incorporation into PI. For PC labelling higher rates of arachidonate incorporation were evident at the higher concentrations of 1-acyl-GPC and the superiority over oleate was not as marked as that seen in PI labelling.

Acylation↗
PubMed1986

The effects of pH, buffers, and fatty acid concentration on the incorporation of radioactive arachidonate into endogenous neuronal nuclear lipids.

Using neuronal nuclei (N1) isolated from cerebral cortices of 15-day-old rabbits the incorporation of [3H]arachidonate into N1 lipids was followed in vitro. Arachidonate was principally incorporated into triacylglycerol and phosphatidylinositol. When low concentrations (32 mM) of Tris-HC1 (pH 7.4) were used, rates of total arachidonate incorporation were small and phosphatidylinositol received the bulk (greater than 84%) of the arachidonate. When the concentration of Tris-HC1 (pH 7.4) or, in certain cases, the concentration of arachidonate was increased, there was a rise in total arachidonate incorporation into N1, with an increasing proportion of radioactivity entering triacylglycerol until it was the predominantly labelled lipid. Using other buffers (phosphate, imidazole, HEPES, pH 7.4), the shift from phosphatidylinositol to triacylglycerol as principal labelled lipid, with buffer concentration, was not as marked as with Tris-HC1 (pH 7.4). When the buffer concentration was maintained at 107 mM and the pH was lowered to 6.5, the three amine-containing buffers showed a sizeable decline in arachidonate incorporation into N1 lipids and a corresponding decrease in triacylglycerol labelling. The proportion of the total radioactivity in N1 phosphatidylinositol rose as the pH declined. Of the buffers used, Tris-HC1 showed the greatest changes over the pH range. Based upon pK values for the amine buffers, it is suggested that an increased proportion of the protonated amine may be inhibitory to arachidonate incorporation in N1. Studies of acyl-CoA synthetase in N1 indicated this enzyme as the site of the inhibition.

Animals↗
PubMed1985

The CMP-stimulated production of diacylglycerol and CDPdiacylglycerol in neuronal nuclei labelled with radioactive arachidonate.

A neuronal nuclear fraction (N1), isolated from immature rabbit cerebral cortex, was preincubated with [3H]arachidonate, ATP, CoA, Mg2+ and 1-acyl-sn-glycero-3-phosphocholine or 1-acyl-sn-glycero-3-phosphoinositol. Using the former lysophospholipid, a sizeable incorporation of radioactivity was seen in N1 phosphatidylcholine. In subsequent incubations in the presence of CMP and EGTA, there was a generation of radioactive diacylglycerol in N1 and a corresponding decline in phosphatidylcholine radioactivity. Both these changes could be blocked by the addition of CDPcholine. In incubations using N1 phosphatidylinositol or phosphatidylethanolamine prelabelled with [3H]arachidonate, no evidence was found to support a direct generation of diacylglycerol from these phospholipids. The back reaction of cholinephosphotransferase in N1 is likely the principal source of diacylglycerols bearing arachidonate. Using either lysophospholipid in the preincubations described in the opening sentence, more than half of the incorporated radioactivity derived from [3H]arachidonate was found in N1 phosphatidylinositol. In subsequent incubations with EGTA and CMP there was a production of radioactive CDPdiacylglycerol and a decline in radioactive phosphatidylinositol. Both events could be blocked by the presence of myo-inositol. Radioactive CDPdiacylglycerol, produced in N1 in the presence of CMP and EGTA, was converted back into phosphatidylinositol by the addition of myo-inositol. The production of CDPdiacylglycerol is likely the result of the back reaction of CDPdiacylglycerol:inositol phosphatidate transferase in N1.

Animals↗
PubMed1984

Phosphatidylcholine as a source of diacylglycerols in neuronal nuclei incubated in the presence of EGTA and CMP.

A neuronal nuclear fraction (N1), isolated from immature rabbit cerebral cortex, was preincubated with 1-[14C]palmitoyl-sn-glycero-3-phosphorylcholine and oleoyl-CoA. Most of the radioactivity was recovered in N1 phosphatidylcholine, and subsequent incubations in the presence of EGTA and CMP indicated an increase in radioactivity in N1 diacylglycerol and triacylglycerol which was matched by a decline in the labelling of N1 phosphatidylcholine. N1 phosphatidylcholine was also prelabelled using [14C]oleate and 1-acyl-sn-glycero-3-phosphorylcholine in vitro, or by intrathecal injection of [3H]oleate prior to N1 isolation. In the following incubations with EGTA and CMP there was a good correspondence between the radioactive decline in N1 phosphatidylcholine and the increase in radioactivity in N1 diacylglycerol. In all these experiments the generation of radioactive diacylglycerol depended upon the presence of EGTA and CMP in the incubations and could be largely inhibited by the addition of CDP-choline. During the prelabelling procedures noted above, other complex lipids had less of the total radioactivity than phosphatidylcholine and showed little or no decline in radioactivity in the presence of EGTA and CMP. In N1 preincubations with [14C]oleate and lysophosphatidylethanolamine, phosphatidylethanolamine could be more highly labelled than phosphatidylcholine, but in subsequent incubations with EGTA and CMP no decline was seen in phosphatidylethanolamine radioactivity. It is concluded that the back reaction of cholinephosphotransferase in N1 represents an active route for the production of diacylglycerols bearing palmitate and/or oleate.

Animals↗
PubMed1984

An increased incorporation of fatty acid into triacylglycerols of neuronal nuclei in vitro in the presence of CMP and EGTA.

Neuronal nuclei (N1) were isolated from cerebral cortices of 15-day-old rabbits. With the addition of both EGTA and CMP the incorporation of radioactive oleate into N1 triacylglycerols in vitro (in the presence of ATP, CoA, and MgCl2) was increased threefold. The same large increase could not be achieved using citrate or EDTA in the presence of CMP or using AMP, UMP, or TMP in the presence of EGTA. The increased labelling of N1 triacylglycerols could be greatly reduced when CDP-choline was added to incubations containing EGTA and CMP. Levels of endogenous N1 diacylglycerols increased threefold following a 10-min incubation in the presence of buffer (pH 7.4) and MgCl2, when CMP and EGTA were also added. Of the major N1 phospholipids, phosphatidylcholine was most similar in fatty acid composition to the enlarged endogenous diacylglycerol pool. The rate of formation of oleoyl-CoA in fraction N1 was not significantly changed by the presence of EGTA and CMP. Rates of triacylglycerol labelling could only be modestly increased when EGTA and CMP were added to incubations containing N1 samples with artificially enlarged endogenous diacylglycerol pools (produced by phospholipase C preincubations). It is suggested that EGTA, as a Ca2+ chelator, and CMP, as a substrate, may allow an enhanced diacylglycerol production mediated by the back reaction of cholinephosphotransferase in N1. The endogenous N1 diacylglycerol produced in the absence of EGTA and CMP may come from another metabolic route.

Animals↗