title: Ultracentrifugation of concentrated biopolymer solutions and effect of ascorbate.
abstract: Highly concentrated solutions of bovine methemoglobin, human transferrin, proteoglycan-protein complex from bovine cartilage, and human hyaluronate were run to equilibrium in the preparative ultracentrifuge. The mass fraction, wo, of water in the compact part of the sediment ("the pellet") was studied as a function of the centrifugal force, ionic strength and pH. For the proteins, wo was close to 0.4 and varied only slightly on variation of the ionic strength and the force. For the proteoglycan-protein complex, wo was close to unity at low force but decreased sharply with increasing force, a finding which agrees well with the specific physical properties of the cartilage matrix. For hyaluronate, wo exceeded 0.8 even at the highest forces, but decreased sharply with increasing ionic strength. There appeared to be a relationship between wo and the carbohydrate mass fraction, wc, of the dry polymer material, wo increasing linearly with wc at 440,000g. A series of biologically or pharmacologically interesting substances was tested for a possible effect on wo of hyaluronate, and it was found that the addition of ascorbate (0.2 g/liter) caused a reduction of 0.040 in wo, independent of the force at which this parameter was measured. Simultaneously, the sedimentation coefficient was doubled. These findings suggest that, on reacting with ascorbate, the hyaluronate molecule changes from a random coil to a more compact molecule.
mesh_terms: D000818:Animals; D001205:Ascorbic Acid; D055592:Biophysical Phenomena; D001703:Biophysics; D002417:Cattle; D005782:Gels; D006801:Humans; D008706:Methemoglobin; D011509:Proteoglycans; D014168:Transferrin; D014461:Ultracentrifugation; D014867:Water
chemical_list: D005782:Gels; D011509:Proteoglycans; D014168:Transferrin; D014867:Water; D008706:Methemoglobin; D001205:Ascorbic Acid