Preheat oven to 350 degrees. Spray an 8 1/2 by 4 1/2 inch loaf pan with nonstick cooking spray. In a bowl, combine flour, baking powder, baking soda, salt and mace. Mix well and set aside. In a mixing bowl, cream margarine and sugar together until smooth. Add egg whites and vanilla; blend until smooth. Alternately add flour mixture and buttermilk to batter in two additions each, blending well after each addition. Spoon batter into prepared pan and bake for 1 hour. Let cake cool before slicing. This was a first place winner in the pound cake division at the Del Mar county fair,1993. Jo Anne Merrill