Section 3B. All interests in real estate situated within the commonwealth heretofore or hereafter acquired by any corporation by eminent domain and all such interests in real estate heretofore or hereafter purchased by any corporation when it could have been acquired by eminent domain shall, unless expressly exempt by the charter of such corporation or by statute, be taxed to such corporation. This section shall not apply to real estate of the commonwealth or of any of its political subdivisions; nor shall it apply to real estate of a railroad corporation, which shall continue to be governed by section eighty-seven of chapter one hundred and sixty and any other provisions of law applicable thereto.