The brain cholecystokinin-converting enzymes that cleave intact cholecystokinin to its COOH-terminal dodecapeptide and octapeptide also cleave the synthetic dipeptides Arg-Ile (or Arg-Val or Arg-Leu) and Arg-Asp, respectively. Thus, they are not hormone-specific enzymes but are bond-specific. Ultracentrifuge studies demonstrate that there is Arg-Ile hydrolase activity associated with a protein greater in molecular weight than gamma globulin and that both Arg-Ile and Arg-Asp hydrolase activities are associated with one or more proteins between albumin and gamma globulin in molecular weight.