The influence of pH, dye, and salt concentration on the dye binding of modified and unmodified fibrin.

The combination of cationic and anionic dyes with proteins of tissues is difficult to interpret chemically because the reactions depend upon many factors. Among these are the physicochemical conditions of staining and the chemical structure, purity, and physical &ate of the pr0tein.l The study of these factors may be simplified by employing “model tissues” but the solid proteins heretofore available for such study (6-9) have certain inherent disadvantages (e.g., wool is a highly specialized fibrous protein and gelatin a degraded one). However, fibrin, a solid protein recently made available in the form of a film (10, ll), is better suited for this purpose. Although it is in a solid and insoluble state, fibrin film must be considered a native undenatured protein, since the fibrinogen from which it is prepared is completely soluble and the conversion of fibrinogen into fibrin by homologous thrombin is chemically identical with the physiological formation of fibrin within the body. Homogeneous sheets of film may be prepared at uniform and desirable thicknesses, and these sheets may be stained under suitable experimental conditions. The amount of dye combined with the fibrin may be measured photometrically. In the present report, the interactions of fibrin with cationic and anionic dyes and the effects thereupon of variations of concentration of dye, of ionic strength, and of pH of the staining solution will be considered. The effects of three denaturing treatments upon the subsequent interaction of fibrin and dye will also be described.2