The importance of azo dyes in biology and medicine has been extensively reported in the literature. Amongst them congo red and methyl orange are of great physiological importance 1-5. Methyl orange has been particularly employed in basic physiological studies to elucidate the mode of interaction between the dye molecules and the proteins 6-15. Quantitative studies on the interaction of methyl orange 16-27 and congo red 28-32 with various proteins have also been carried out.
In the present communication we report the results of our investigations on the interaction of congo red and methyl orange dyes with fibrillar and globular proteins. For the fibrillar protein, transfusion gelatin was chosen since it is a well characterised protein of low molecular weight while for the globular protein, ovalbumin was found to be quite suitable.
EXPERIMENTAL
Materials
Transfusion gelatin 33 (concentration 6~o, mol.wt.=75,000) supplied by the Director, National Chemical Laboratory, Poona, India, was used as such. Ovalbumin (mol.wt=45,000) was an E. Merck product. Its solution was prepared in doubly distilled water. The solution was centrifuged and its concentration determined by drying a known aliquot in an electric oven at 105Β°C.
Methyl orange and congo red were B.D.H. products. Clark and Lubs buffer 3~ containing KHzPO 4 and NaOH was used throughout these investigations. The buffer constituents were of A.R. grade and all the solutions were made in doubly distilled water.
Apparatus
Polarographic measurements were made with a Heyrovsky LP 55A polarograph operated manuaily in conjunction with a Scalamp Pye gaNanometer in the external circuit. An H-type polarographic cell was found to be suitable for deaeration of the protein solution without denaturation. Purified nitrogen was passed for 15 min in each case to remove oxygen. Triply distilled mercury was used for the dropping electrode. The capillary used had a flow rate of 2.8 mg s-1 with a drop time of 3.5 s. The temperature of the solution was maintained at 25 +0.1Β°C by keeping the cell immersed in a thermostatic water bath.