Mo. Rev. Stat. § 215.150

The commission, subject to the terms of any agreements with noteholders or bondholders as may then exist, shall have power out of any funds available therefor and not otherwise committed, to purchase notes or bonds of the commission which shall thereupon be cancelled at a price not exceeding: (a) if the notes or bonds are redeemable, the redemption price then applicable plus accrued interest to the next interest payment date thereon, or (b) if the notes or bonds are not then redeemable, the redemption price applicable on the first date after such purchase upon which the notes or bonds become subject to redemption plus accrued interest to such date.