Human blood has been shown to contain two different kinin precursors, i.e0 the high
and the low molecular mass kininogen0 These two kininogens release the same kinins,
with the starting sequences Met-Lys-Arg-Pro-, Lys-Arg-Pro- or just Arg-Pro-depending
on the releasing enzyme. The kinin starting with Arg-Pro- is denoted as bradykinin.
In rats a different kininogen, called T-kininogen, is also present, especially as
the major acute-phase protein in this species. The corresponding kinin, T-kinin, has
the starting sequence Ile-Ser-Arg-Pro-. This type of kininogen or kinin has previously
never been detected in human tissues. However, during the course of the present study
evidence for existance of a third human kininogen, giving rise to human T-kinin, was
obtained.
Ascites from patients with metastatic ovarian carcinoma has been shown to contain
high amounts of vascular permeability-increasing activity as determined by a rat skin-Evans
blue test. When the ascites was fractionated by gel filtration followed by reversed-phase
high-performance liquid chromatography (HPLC) a component could be isolated which
by its total sequence and amino acid composition was identified as Ile-Ser-bradykinin.
Several degradation products of this kinin were also detected as separate components
in the chromatographies. The human Ile-Ser-bradykinin appeared on reversed-phase HPLC
in the same position as synthetic T-kinin. It could be differentiated in this chromatography
system from Met-Lys-bradykinin, Lys-bradykinin and bradykinin. It may be assumed that
human Ile-Ser-bradykinin is released_ from a third, so far unidentified human kininogen
which is only or predominantly expressed under certain pathophysiological conditions,
and that therefore this new kinin might be employed as a tumor marker.
