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X Y He

Publications and source records attributed to X Y He.

66 records · Page 4Linked to original sources
PubMed1988

Evidence that the fadB gene of the fadAB operon of Escherichia coli encodes 3-hydroxyacyl-coenzyme A (CoA) epimerase, delta 3-cis-delta 2-trans-enoyl-CoA isomerase, and enoyl-CoA hydratase in addition to 3-hydroxyacyl-CoA dehydrogenase.

Genetic complementation of a mutant defective in fatty acid oxidation (fadAB) with plasmids containing DNA inserts from the fadAB region of the Escherichia coli genome was studied. The mutant containing the hybrid plasmid with a 5.2-kilobase (kb) PstI-SalI fragment was found to overproduce 3-hydroxyacyl-coenzyme A (CoA) epimerase and delta 3-cis-delta 2-trans-enoyl-CoA isomerase as well as three other beta-oxidation enzymes by 16- to 18-fold compared with the wild-type parental strain LE392. The purification of a fully functional multienzyme complex of fatty acid oxidation from the transformant ultimately established that the 5.2-kb DNA fragment contained an entire fadAB operon. Since immunotitration of cell extracts with antibodies against the fatty acid oxidation complex proved that all 3-hydroxyacyl-CoA epimerase and delta 3-cis-delta 2-trans-enoyl-CoA isomerase activities were associated with the complex, no genetic loci other than the fadAB operon encoded these two enzymes. Moreover, the binding of antibodies caused parallel inhibition of four component enzymes, whereas 3-ketoacyl-CoA thiolase activity was slightly increased. These findings support the suggestion that the epimerase and isomerase as well as enoyl-CoA hydratase and L-3-hydroxyacyl-CoA dehydrogenase are located on the same polypeptide. The results of this study, together with published data (S.-Y. Yang and H. Schulz, J. Biol. Chem. 258:9780-9785, 1983), lead to the conclusion that 3-hydroxyacyl-CoA epimerase, delta 3-cis-delta 2-trans-enoyl-CoA isomerase, and enoyl-CoA hydratase in addition to 3-hydroxyacyl-CoA dehydrogenase are encoded by the fadB gene.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1987

Fatty acid oxidation in rat brain is limited by the low activity of 3-ketoacyl-coenzyme A thiolase.

In an attempt to clarify why the brain oxidizes fatty acids poorly or not at all, the activities of beta-oxidation enzymes present in rat brain and rat heart mitochondria were measured and compared with each other. Although the apparent Km values and chain-length specificities of the brain and heart enzymes are similar, the specific activities of all but one brain enzyme are between 4 and 50% of those observed in heart mitochondria. The exception is 3-ketoacyl-CoA thiolase (EC 2.3.1.16) whose specific activity in brain mitochondria is 125 times lower than in heart mitochondria. The partially purified brain 3-ketoacyl-CoA thiolase was shown to be catalytically and immunologically identical with the heart enzyme. The low rate of fatty acid oxidation in brain mitochondria, estimated on the basis of palmitoylcarnitine-supported respiration and [1-14C]palmitoylcarnitine degradation to be less than 0.5 nmol/min/mg of protein, may be the consequence of the low activity of 3-ketoacyl-CoA thiolase. Inhibition of [1-14C]palmitoylcarnitine oxidation by 4-bromocrotonic acid proves the observed oxidation of fatty acids in brain to be dependent on 3-ketoacyl-CoA thiolase and thus to occur via beta-oxidation. Since the reactions catalyzed by carnitine palmitoyltransferase (EC 2.3.1.21) and acyl-CoA synthetase (EC 6.2.1.3) do not seem to restrict fatty acid oxidation in brain, it is concluded that the oxidation of fatty acids in rat brain is limited by the activity of the mitochondrial 3-keto-acyl-CoA thiolase.

Acetyl-CoA C-Acyltransferase↗
PubMed1987

Evidence for structural changes in dermatan sulfate and hyaluronic acid with aging.

Three dermatan sulfates (DS18, DS28, and DS35) were isolated from women's skin of ages 19 +/- 2.5, 35 +/- 3.5, 47 +/- 1.7, 60 +/- 0.8, and 75 +/- 5 years. They sequentially precipitated with 18, 28, and 35% ethanol. Their sulfate content was: 23.5, 25.3, and 29.0% (w/w) for DS18 at ages 19-35, 47, and 60 years, respectively; 29.0, 24.0, and 18.8% for DS28; and 18.0, 20.0, and 20.6% for DS35 at ages 19-47, 60, and 75 years, respectively. Both DS18 and DS28 decreased, respectively, from 0.030% (of wet-skin weight) to traces at age 75, and from 0.020 to 0.010% at 60 years. At age 75, DS28 apparently increased by 30%. The DS35 values (traces-0.006%) had no age-related trend. Hyaluronic acid (HA) precipitated with 45% ethanol, was 0.030% of skin-weight at ages 19-47, and decreased to 0.015 and 0.007% at 60 and 75 years, respectively. Its electrophoretic mobility was slower at age 47. In the oldest group, i.r. spectra of HA and DS35 displayed no bands at 1650-1600, 1380, and 1320 cm-1, and a new band at 1560 cm-1. Moreover, ninhydrin-positive material of HA and DS35 increased by 75 and 95%, respectively, and the reducing GlcNAc content of HA decreased. These data showed three chemically different dermatan sulfates (two of which were preponderant) and N-deacetylation of HA and DS35 of the oldest group. After age 47, total DS and HA considerably decreased, DS18 and DS35 were oversulfated, and DS28 became undersulfated with aging.

Adult↗
PubMed1986

Chemical alterations of hyaluronic acid and dermatan sulfate detected in aging human skin by infrared spectroscopy.

Age-mediated deacetylation of hyaluronic acid and dermatan sulfate, and shift of sulfate ester configuration were indicated by infrared spectroscopy. Hyaluronic acid and the three dermatan sulfates (DS18, DS28 and DS35), sequentially precipitated from adult skin with 18%, 28% and 35% ethanol, were analyzed at varying ages. At age 75 years, loss of infrared bands in the 1,650-1,600 cm-1 region, at 1,380 cm-1 and 1,320 cm-1 and appearance of a band at 1,560 cm-1 were characteristic of hyaluronic acid and DS35; moreover, in DS28 and DS35 the intensities of the bands at 840 cm-1 and 860 cm-1 were, respectively, decreased and increased. A low intensity band in the 805-785 cm-1 region was observed in the spectra of DS18 (19-35 years), DS28 (70-80 years) and DS35 (all ages). It intensified in DS28 of the 80-year-olds. In the 75 +/- 5-year-old group, ninhydrin-positive material of hyaluronic acid and DS35 increased, while reducing GlcNAc of hyaluronic acid decreased. The data demonstrated hyaluronic acid and DS35 deacetylation and suggested a decrease of equatorial sulfates with infrared band at 840 cm-1 and an increase of axial sulfates with band at 860 cm-1 in DS28 and DS35 of the 75 +/- 5-year-old set. Equatorial Equatorial sulfates with band in the 805 +/- 785 cm-1 region apparently decreased in DS18 after 35 years and increased in DS28 of the oldest group.

Adult↗