thiourea in 2D page - What's it for? (Jul/15/2010 )

Is the thiourea included to scavenge excess alkylating agent prior to running the 2nd dimension of 2D gels?

While I suppose thiourea can react with IAA, excess IAA probably doesn't hinder PAGE. I'm not sure that it's known what exactly thiourea does, biochemically speaking, in 2D PAGE.