Home cholesterol testing.

Lipid extracts of liver tissue from normal donors and from patients with acute liver failure were analyzed by 13C NMR and 1H NMR at 9.4 T. The spectra allowed estimation of (i) the free fatty acid to total fatty acid chains ratio, (ii) the polyunsaturated to monounsaturated lipids ratio, (iii) the glycerophospholipids to triacylglycerols ratio, (iv) the total cholesterol to total fatty acids molar ratio, (v) the acylcholesterol to cholesterol ratio, (vi) the phosphatidylcholine to phosphatidylethanolamine molar ratio, and (vii) the unsaturation ratio of the fatty acid chains. The values obtained for normal livers agree with literature data on lipid composition obtained by other techniques. The two pathologic livers differ from the normal in the composition of some lipids and show a higher free fatty acid to total fatty acid chains ratio and a lower polyunsaturated to monounsaturated lipid ratio, a lower acylcholesterol to cholesterol ratio, and a lower phosphatidylcholine to phosphatidylethanolamine ratio, whereas the ratio of total cholesterol to fatty acids and the unsaturation ratio remained unchanged. The detailed assignment of the 13C NMR spectra of lipid extracts from normal and pathologic human liver may contribute to direct future research programs on 13C NMR spatially localized spectroscopy of the liver in vivo.

Cholesterol↗

PubMed1996

Reaction mechanism of human DNA repair excision nuclease.

Nucleotide excision repair consists of removal of the damaged nucleotide(s) from DNA by dual incision of the damaged strand on both sides of the lesion, followed by filling of the resulting gap and ligation. In humans, 14-16 polypeptides are required for the dual incision step. We have purified the required proteins to homogeneity and reconstituted the dual incision activity (excision nuclease) in a defined enzyme/substrate system. The system was highly efficient, removing >30% of the thymine dimers under optimal conditions. All of the six fractions that constitute the excision nuclease were required for dual incision of the thymine dimer substrate. However, when a cholesterol-substituted oligonucleotide was used as substrate, excision occurred in the absence of the XPC-HHR23B complex, reminiscent of transcription-coupled repair in the XP-C mutant cell line. Replication protein A is absolutely required for both incisions. The XPG subunit is essential to the formation of the preincision complex, but the repair complex can assemble and produce normal levels of 3'-incision in the absence of XPF-ERCC1. Kinetic experiments revealed that the 3'-incision precedes the 5'-incision. Consistent with the kinetic data, uncoupled 5'-incision was never observed in the reconstituted system. Two forms of TFIIH were used in the reconstitution reaction, one containing the CDK7-cyclin H pair and one lacking it. Both forms were equally active in excision. The excised oligomer dissociated from the gapped DNA in a nucleoprotein complex. In total, these results provide a detailed account of the reactions occurring during damage removal by human excision nuclease.

Cholesterol↗