Several years ago it was reported that poly-a,L-glutamic acid (PGA) would form complexes with several symmetrical dyes, among them acridine orange (A0).'v2 Although the dye binds to either the helical or random coil conformations in water solution, the very interesting observation was made that A 0 exhibits optical activity only when bound to helical polymer. Similar observations have been made with AO: DNA complexes3; only the native, helical DNA solutions yield optical activity in the absorption bands of the bound dye. Largely on the basis of these results, others4-6 have recently begun to infer that some type of helical order might well exist in various polysaccharides, such as heparin and chondroitin sulfate. These polymers also yield optically active complexes with a number of symmetrical dyes. We have been investigating the optical properties of the AO: PGA system in some detail, and wish to give a preliminary report, on the observation of an optically active complex between A 0 and PGA in the random coil pH region.A given A 0 : PGA complex solution can be conveniently described by specifying the total dye molarity [D], theratioof glutamyl residues to dye molecules, RID, and the usual solution parameters, pH, ionic strength, etc. Spectroscopic titrations of A 0 solutions with PGA reveal that, at R/D values greater than 5, essentially all the available dye has been bound to the PGA throughout the pH range reported here.7 No further changes in the dye absorption spectrum take place until an extreme excess of PGA is added (RID

SynopsisBy iiieaiis of fiuoresceiicc, absorptioii, and acid-base t itrittioiis, it tias bee11 showii t 1i:tt there is a one-to-one corresporideiice between free carboxylates arid boiiiid aciiditie oiaiige in the dye-polyacid complex. Coritmry to expections, stackiiig coefticierits for 1 he dye were found t,o be virt,ually the same on binding 1.0 the helical or coiled polyacid, iiidicatirig a strong similarity in the binding sit,es for both forms of the polyelectrolyte.

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