Preparative ultracentrifuge, binding

Several methods revealed that PECs between strong polyelectrolytes have a 1 1 end point stoichiometry and also a 1 1 stoichiometry of ionic binding under full release of the low molecular counterions at nonstoichiometric mixing ratios. However, it remains an open question whether the major component in such systems is bound in excess in the PEC structures, giving them a net excess charge. To solve this problem, viscometry, analytical or preparative ultracentrifugation, and fractionation techniques in combination with analyzing methods can be employed. 

Preferential binding in PEC formation between PDADMAC and mixtures of Na lignosulfonate and Na cellulose sulfate or Na carboxymethylcellulose was studied in [64] in relation to the ionic strength by preparative ultracentrifugation and an analysis of the supernatants by UV spectroscopy. 

Figure 9-15. Poly I,G-effected separation of the complementary strands of A phage DNA in preparative and analytical CsCl gradients. Upper trace represents the absorbance (260 nm) of the 4-drop (50 tl) fractions (total volume 2.5 ml) measured in a 20 /u.1 microcuvette (2 mm light path). Lower trace represents the microdensitometric tracing of the photograph of the same undiluted material banded in the analytical ultracentrifuge (4°C, 3 mm cell) with added density marker DNA (Cytophaga johnsonii, 1.6945 g/cm dashed line). Peak C contains the DNA strands C, which preferentially bind poly I, G the complementary strands W band under peak W. Symbols dN and NN indicate the positions (densities) of the denatured and native Acbj DNA, respectively. [From Z. Hradecna and W. Szybalski, Virology, 32 633 (1967).]...

The data in Fig. 1 illustrate that the thyroid-stimulating activity of the immunized rabbit serum is not inhibited by a dose of antithyrotropin antiserum which inhibited the concentration of rabbit thyrotropin giving a similar 2 hr response in the bioassay. Further, the activity was apparently bound to thyroid microsomes when the extract of rabbit serum was incubated with a human thyroid microsome preparation and the microsome pellet resedimented by ultracentrifugation, the supernatant contained no thyroid stimulating activity [distinct from results (not shown) found with a human liver microsome preparation which did not bind the thyroid stimulator]. The importance of the latter data is marginal since. 

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