Dissolve yeast in warm water; let stand for 5 minutes. Stir in buttermilk and set aside.
In a large bowl, combine flour, baking powder, salt, baking soda and sugar; cut in shortening with a pastry blender until mixture is crumbly. Make a swell in center of mixture; add reserved yeast mixture; stir just until dry ingredients are moistened.
Turn dough out onto a lightly floured work surface, and knead lightly 3 or 4 times. roll dough to 1/2-inch thickness; cut with a 2-inch biscuit cutter. Place on lightly greased baking sheets. Cover and let rise in a warm place, free of drafts, for 30 minutes.
Bake at 400° F - 205*C) for 10 to 12 minutes or until biscuits are lightly browned.Makes 3 1/2 dozen