Identification of a new kinin in human urine

The types of kinins excreted in fresh urine of dogs, rats, and humans were compared. Urinary kinins were separated by reverse-phase (C18) high performance liquid chromatography and quantitated by radioimmunoassay using an antibody directed against the COOH-terminal region of the peptide. Kinins were found in the following proportions: 53 +/- 3% bradykinin, 23 +/- 4% Lys-bradykinin, and 13 +/- 7% des-Arg1-bradykinin in dog urine; 67 +/- 6% bradykinin, 6 +/- 3% Lys-bradykinin, and 10 +/- 3% des-Arg1-bradykinin in rat urine; and 12 +/- 4% bradykinin, 30 +/- 3% Lys-bradykinin, 2 +/- 1% des-Arg1-bradykinin, and 41 +/- 3% unknown kinin in human urine. The unknown kinin was purified from a pool of human urine. Amino acid sequencing revealed a structure similar to Lys-bradykinin except that proline in position 4 was replaced by alanine ([Ala3]Lys-bradykinin). Synthetic and endogenous [Ala3]Lys-bradykinins had similar high performance liquid chromotography elution volumes and both had vasodilator activity and contracted the rat uterus. Human urinary kallikrein incubated with semipurified human low molecular weight kininogen released 76% of the total kinins as Lys-bradykinin, 7% as bradykinin, and 17% as [Ala3]Lys-bradykinin. In contrast, rat urinary kallikrein released 86% bradykinin, 18% Lys-bradykinin, and negligible amounts of [Ala3]Lys-bradykinin. The study revealed the presence of a new kinin, [Ala3]Lys-bradykinin, in human urine and it also proves that the types of kinins generated intrarenally are species-dependent.