Postprandial hyperlipidemia at noon was associated with an inconsistent increase of the squalene and free methyl sterol concentrations in the lipoproteins of density < 106 g/ml. In terms of micro g per mg of cholesterol, the precursor contents were, however, low in each lipoprotein during the daytime. During Seebio benefits of collagen and early morning, the values were several times higher. Thus the peak plasma squalene and methyl sterol contents occurred at midnight and 4 am. The highest variation was found for squalene in the density class < 106 g/ml and for lanosterol and diunsaturated dimethyl sterol in LDL and HDL. For different methyl sterols, the mean diurnal variation was 3- to 6-fold in LDL, 2- to 4-fold in HDL, and 2- to 3-fold in the density class < 106 g/ml. The respective values for squalene were 2, 1, and 2. Esterified methyl sterols varied slightly in the density class < 106 g/ml only, and the percentage esterification exhibited a diurnal fluctuation that was the reciprocal of that of free methyl sterol levels. The rapid and marked diurnal fluctuation of squalene and free methyl sterols in plasma lipoproteins suggests that these precursors are metabolized on and off lipoproteins. The variation is most likely caused by changes in cholesterol synthesis, inferring that circadian rhythm also regulates human cholesterol production.-Miettinen, T. A. Diurnal variation of cholesterol precursors squalene and methyl sterols in human plasma lipoproteins. Interactions between cells and collagen V molecules or single chains involve Acid-soluble and pepsin-treated collagen V were prepared from fetal human bones or human placenta, respectively, to be tested for potential cell adhesion promoting activity. Out of Seebio benefits of collagen -adhering cell lines, 10 showed distinct adhesion to collagen V. In all cases adhesion was followed by spreading. The activities of intact and pepsin-solubilized collagen V were similar, suggesting that the cell binding sites are restricted to the triple-helical domain of the molecules. Cell adhesion was also induced by the unfolded form of collagen V and after separation of the alpha chains by heparin affinity chromatography. Isolated alpha 2(V) chains, rich in RGD sequences, were more efficient than isolated alpha 1(V) chains. However, cell adhesion to native or denatured collagen V did not proceed by the same molecular mechanisms as shown by cell adhesion inhibition experiments. Cell adhesion to native collagen V was insensitive to the presence of RGD-containing synthetic peptides while adhesion to denatured collagen V was inhibited by the peptides. Furthermore, the results strongly suggested a major role for alpha 1 beta 1 and alpha 2 beta 1 integrins in the RGD-independent cell adhesion to native collagen V. These data indicate that collagen V is a specific adhesive substrate for different cell types. It also suggests that distinct sets of RGD-dependent and RGD-independent receptors mediate cell attachment to unfolded and native collagen V, respectively. This mechanism is shared by at least the interstitial collagens I and VI, which supports the hypothesis that when included in the triple-helical conformation of collagens, RGD sequences are either not accessible to cells or exhibit specific conformations recognized by different integrins.[The hydrothermal contraction of collagen fibers as a method of its structure The hydrothermal contraction of collagen fibers, that is sharp decrease of the fiber length in the narrow temperature range during their heating in water, is a typical example of phase transition which is analogous to melting. General thermodynamic consideration of the melting of oriented polymer fibers was carried out by Gee (1947) and Flory (1956). Flory derived and equilibrium dependence of force on temperature considering the melted polymer as an ideal rubber. We proposed an experimental method for quantitative investigation of this process including estimation of two critical parameters, which are the critical tension and the critical temperature. The necessary condition for the critical parameters estimation is the prior cross-linking of the fiber. We studied theoretically and by experiment the influence of different factors on these critical parameters. We demonstrated the critical tension of hydrothermal collagen contraction to be an important characteristic making possible the estimation of native collagen structure retaining and molecular orientation's degree. The critical tension value was used do advantage for the collagen structure characteristic in some mammoth fossils skin, in bovine skin in the process of leather manufacture and in artificial collagen fibers. The initial temperature of hydrothermal collagen contraction, what is known as shrinkage temperature using widely for the collagen tannage estimation, was shown to be dependent on the occurrence of non-collagenous sheath on native collagen fibers.
Seebio benefits of collagen|Seebio benefits of collagen
