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JBC, Vol. 250, Issue 19, 7780-7787, Oct, 1975
M. Oho, P. Riquetti and B. G. Hudson
Bovine glomerular basement membrane was extracted with 6 M guanidinium
chloride and the soluble material fractionated on a Bio-Gel A-1.5m column
in 1% Na dodecyl-SO4. A single component was obtained by reduction of a
selected column fraction with 2-mercaptoethanol followed by chromatography
on an analytical Bio-Gel A-1.5m column and shown to be homogenous by
electrophoresis and ultracentrifugation. It consists of 90% protein and
8.6% carbohydrate by weight. The amino acid composition is characterized by
the presence of low amounts of hydroxyproline and hydroxylysine, and
substantial amounts of aspartic acid, glutamic acid, half-cystine, and
glycine. It contains all the monosaccharide constituents present in the
whole basement membrane indicating the presence of both
heteropolysaccharide and disaccharide units; the presence of the latter
unit was demonstrated unequivocally by ion exchange chromatography. The
component contains 1 heteropolysaccharide unit and 4 dissaccharide
units/molecule of Mr equals 70,000. The molecular weight of component VII
was determined by several methods. Molecular weight values of 68,000 +/-
3,000 and 72,000 +/- 2,000 were determined in 6 M guanidinium chloride by
the methods of sedimentation equilibrium and gel filtration chromatography,
respectively, and values of 136,000 +/- 3,100 and 140,000 +/- 2,000 were
determined in 1% Na dodecyl-SO4 by the methods of polyacrylamide gel
electrophoresis and gel filtration chromatography, respectively. Circular
dichroism spectra indicate that component VII assumes a random coil
conformation in 6 M guanidinium chloride and a more disordered conformation
in 1% Na dodecyl-SO4 than standard proteins used in calibration of
polyacrylamide gels and gel filtration column. These results indicate that
the minimal molecular weight of component VII is about 70,000 and that the
anomalous behavior in Na dodecyl-SO4 is due in part to its conformation.
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