What kind of fabric/fiber is it, and what kind of beading? Is the purse in good condition, other than the yellowing?
If cotton, soaking in a solution of hot Oxyclean may get rid of the stain-- I was able to treat vintage crocheted doilies sucessfully, but it took a few tries to get all of the staining out.
If it is a bead crochet or bead knit purse, it may be either cotton or silk cord-- turn inside out before washing and/or soaking in the Oxyclean.