Subfractionation

As further subfractionation facilitates subsequent studies at a molecular level, further separation into compound groups is applied. For example, the saturated hydrocarbon fraction can be treated with 5 A molecular sieves or urea for the removal of n-alkanes, leaving behind a fraction of branched and cyclic alkanes [7,8]. The procedure is described in the following text in detail. 

Heparin may also be subfractionated on a preparative scale, by precipitation of its sodium or barium salt with ethanol. Whereas sodium salts afford a continuum of species essentially differing in molecular weight,210 the solubility curves of barium salts show discrete steps, indi-... 

It is often important to examine the solids which can be isolated from the supernatant liquors obtained during a fractionation, as it would appear that subfractionation of amylose can occur.28... 

Wibo M, Godfraind T 1994 Comparative localization of inositol 1,4,5-trisphosphate and ryanodine receptors in intestinal smooth muscle an analytical subfractionation study. Biochem J 297 415 -23... 

Primarily through the work of Oncley et al. [for reviews, see references (C4) and (Bll)], relatively simple procedures have been devised for the specific precipitation of the low- or the high-density lipoproteins by the use of polyanions in the presence of divalent cations. It is necessary, however, to purify the preparations thus obtained, but the procedures thus far described do not permit subfractionation of the major lipopro-... 

TABLE 10.25 Mass Concentrations of Individual Genotoxic PAHs and PACs in the Whole Sample and in Subfractionated Extracts,1 Their Absolute Mutagenic Potencies and Potencies Relative to Benzotalpyrene = 1.00, and Contributions of Each to the Overall Total Potency of a Composite Mixture of Ambient Aerosols Collected at Four Urban Sites in Southern California for One Year (1993) and Subjected to Bioassay-Directed Chemical Analysis Using the hlAlv2... 

Isolation, Subfractionation, and Enzymatic Analysis oi Beef Heart Mitochondria... 

The literature abounds with reports of the fractionation of extracts from coal, more specifically to the liquids and solids produced by various coal liquefaction processes (Speight, 1994, and references cited therein). However, to accomplish the subfractionation of the coal extracts, it is preferable to apply (with any modifications noted) a suite of the standard test methods that are often applied to petroleum and its residua. However, before application of any subfractionation procedure to coal extracts, it may be necessary to stabilize the extracts (at a fixed temperature and pressure) to ensure that losses of potentially volatile constituents do not occur during the subfractionation procedure. Once the extracts have been stabilized, it is in order to proceed. 

M18. Mahley, R. W., and Weisgraber, K. H., Subfractionation of high density lipoproteins into two metabolically distinct subclasses by heparin affinity chromatography and Geon-Pevikon electrophoresis. In Report of the High Density Lipoprotein Methodology Workshop (K. Lippel, ed.), pp. 356-366. U.S. Department of Health, Education and Welfare. NIH publication No. 79-1661, Bethesda, Md., 1979. 

T10. Trezzi, E., Calvi, C., Roma, P., and Catapano, A. L., Subfractionation of human very low density lipoproteins by heparin-Sepharose affinity chromatography. J. Lipid Res. 24, 790-795 (1983). 

W12. Weisgraber, K. H., and Mahley, R. W., Subfractionation of human high density lipoproteins by heparin-Sepharose affinity chromatography. /. Lipid Res. 21, 316-325 (1980). 

There is evidence [52] that there are at least two forms of cyt P-450 involved with aromatization. Likewise, there is evidence for different aromatases in human placenta which catalyse the production of oestrone and oestriol from 4-androstenedi-one and 16a-hydroxytestosterone, respectively. Each enzyme system has been subfractionated into its own cyt P-450 and cyt P-450 reductase [107]. This has been supported recently by Purohit and Oakey [108], who measured aromatase activity for 16a-hydroxy-4-androstenedione and 4-androstenedione in the presence or absence of the other substrate. 4-Androstenedione competitively inhibited aromatization of the 16a-hydroxy derivative, with apparent K, essentially the same as its apparent Km, suggesting that both substrates bind and are aromatized independently of each other. The 16a-hydroxy derivative competitively inhibited the aromatization of 4-androstenedione, thus presumably lowering the affinity of the aromatase for the latter. 

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