(a) After incorporation and the issuance of a certificate of authority to an insurance company, the minimum capital stock and surplus of the company may consist only of:
(1) United States currency;
(2) bonds of this state;
(3) bonds or other evidences of indebtedness of the United States the principal and interest of which are guaranteed by the United States;
(4) bonds or other interest-bearing evidences of indebtedness of a county or municipality of this state; and
(5) notes secured by first mortgages:
(A) on otherwise unencumbered real property in this state the title to which is valid; and
(B) the payment of which is insured wholly or partly by the United States.
(b) Not more than 50 percent of the minimum capital stock and minimum surplus of an insurance company may be invested in an investment described by Subsection (a)(5).