This is a product that has been reviewed before on the forum. According to King Arthur, this is the ingredients list:
Perfect Pizza Blend
Item # 3295
Ingredients: King Arthur Unbleached Flour (wheat flour, malted barley flour, niacin, reduced iron, thiamin mononitrate, riboflavin, folic acid), durum wheat flour (milled wheat, niacin, iron, thiamin mononitrate, riboflavin, folic acid), inactive yeast, leavening (monocalcium phosphate, baking soda, cornstarch).
The inactive yeast is most likely dead yeast, and used to soften the dough so that it is extensible. Also, there is a chemical leavening system.