Polyvinylpyrrolidone (PVP) displays strong binding affinities toward various organic anions such as the azo dyes orange II (O-II) and benzopurpurin 4B (BP). The binding equilibria were studied by a conductance method and by a dialysis technique. It was found that one dyestuff ion is bound by chain segments of 7 or 10 monomer units for O-II and BP, respectively. It is believed that the dye ions align themselves with their long axis alongside the polymer chain and are held in place by van der Waals forces. The effect of added potassium chloride on the binding equilibria was studied. The polyelectrolyte character of the PVP-dye complex was demonstrated by its electroviscous effect. A viscosity reduction in the presence of salt was explained as a cross-linking effect due to aggregation of dye ions.(1) This work was supported by the office of the Surgeon General, Dept, of the Army.
Treatment of a solution of rat tail tendon collagen in acetate buffer with a proteolytic enzyme (ficin) led to a monodispersed solution of rodlike particles whose dimensions were 12.6 A. in diameter and 2400 A. in length. Similar enzymic treatment of dispersions of steer tendon collagen fibrils resulted in a disaggregation of the fibrils to a solution of particles of essentially similar dimensions. The nature of the enzymic attack in relation to the structure of the substrate is discussed.
Two modifications of a method are presented for assaying proteolytic enzymes. They differ primarily in the mechanism used for terminating the enzymic reaction, one technique employing trichloroacetic acid (TCA), the other, heat inactivation. Comparative studies reveal that there are two distinct disadvantages in using TCA which are not evident with the heat inactivation procedure. In the first place, TCA does not selectively precipitate residual substrate. Secondly, in the presence of acid, linear alkyl benzene sulfonate and other long chain anionic surfactants interfere with the quantitative determination of enzymic activity. This interference can be falsely interpreted as inhibition of proteolysis. An explanation of the above phenomena is given in the text along with assay results in the presence of metal chelating agents.
An automated biological assay for proteases in detergents was developed. The assay involved enzymic digestion of casein followed by the analysis of the liberated amino groups. Quantitative determination of the proteolytic activity was accomplished by reacting the amino groups with trinitrobenzene‐sulfonic acid (TNBS). An automated system was used to carry out both the digestion and the quantitative color development of the TNBS‐amino group complex. The method is accurate, reproducible, easy to handle, fast and free from interferences by any of the standard detergent ingredients. It may also be used as an investigative tool in enzyme research.
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