The provisions of Sections 89-1-301 through 89-1-329 shall not apply to any mortgage while such mortgage is held by the United States or agency thereof as security or pledge of the maker, its successors or assigns, nor shall the provisions of Sections 89-1-301 through 89-1-329 apply to any mortgage held as security or pledge to secure payment of a public debt or to secure payment of the deposit of public funds.