Preheat oven to 325 degrees. Grease and flour a 9x5-inch loaf pan. In medium bowl, sift the flour, baking powder and salt together. Set aside. In another bowl, cream butter and sugar together. Add eggs, one at a time, mixing well after each addition. Mix buttermilk and lemon juice together in another bowl. Alternately add the dry ingredients and the wet ingredients to the butter and sugar mixture. Add lemon zest and mix, just until smooth. Pour into loaf pan and bake for 55-60 minutes or until tester comes out clean. Cool cake for ten minutes. Mix the powdered sugar and 1/3 cup of lemon juice glaze together with a whisk. Make a few holes in cake with a toothpick and pour glaze over cake. Store the cake covered in the refrigerator after serving.