In 36 patients suffering from chronic renal failure (mean creatinine clearance 26 ml/min), serum silicon levels were significantly increased (mean 0.52 μg/ml compared with 0.265 μg/ml in normals; p < 0.005). Urinary silicon excretion per 24 h was significantly decreased (15.71 mg/24 h compared with 21.4 mg/24 h in normals; p < 0.001). Fractional excretion of silicon (FESi) was significantly increased in chronic renal failure (p < 0.001), with overall tubular secretion of silicon in 33% of patients. Urinary excretion of silicon was significantly related to urinary calcium excretion (p < 0.0001) urinary magnesium excretion (p < 0.0001) creatinine clearance (p < 0.05) and sodium excretion (p < 0.05). It is suggested that urinary silicon is in the form of orthosilicate, principally bound to calcium and magnesium; and that in chronic renal failure the increase in FEsi, and the decrease in absorbed Si from the gastrointestinal tract, moderate the increase in plasma silicon levels and prevent excessive entry of silicon into the tissues.
Nucleoprotein complexes reconstituted from calf thymus DNA and lysine-rich histone (f-1 fraction) in a variety of neutral salts and in dioxane were examined by circular dichroism. The alteration of the DNA ellipticity bands is interpreted as a reflection of conformational change of the DNA in the complexes. Gradient dialysis of DNA and f-1 in various ratios into 0.14 or 0.3 M uni-univalent salt solutions results in circular dichroic spectra which can be approximately ordered according to the lyotropic series. This sequence was found to be, in order of the effect on the DNA circular dichroic spectrum (that is, beginning the sequence with salts that alter the circular dichroism spectra the most): guanidine'HC1 > NHdC1, NH40Ac >> CsCl > KC1, KF > NaOAc, NaBr, NaF, NaCl > LiCl >> NaC104, KCNS, NaI. Most of the effect is exerted through cations.Blkali metal ions enhance the ellipticity changes of complexes to various extents. Ammonium and guanidinium ions cause the largest changes in the circular dichroism; these specific ion effects are remarkable because of the relatively low salt concentration at which they operate. Most anions (OAc-, F-, C1-, Br-) have little effect, except for C104-, CNS-, and I-, which dissociate the complexes. Very low MgClz concentration ( 5 0.006 M ) augments conformational changes; at higher concentration MgClz causes dissociation. Addition of dioxane (up to 40% by volume) enhances distortion of the DNA ellipticity. Different types of complexes result (1) from direct mixing of f-1 histone and DNA in 0.14 iM KaF, (2) from dialysis into 0.01 M NaF, and (3) from dialysis into 0.14 M NaF. Filtration experiments indicate that histone binds to DNA in a partially cooperative manner. f-1-DNA interaction is modified by salt concentration, specific salt effects, dioxane, and manner of complex formation. This complicated behavior indicates that charge attraction between histone and DNA, even when supplemented by hydrophobic bonding, is insufficient to account for the observed circular dichroic changes. Specific association of complexes may be involved, mediated by the presence of various salts.
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