The inositol-phospholipid-accelerated activation of prekallikrein by activated factor XII at physiological ionic strength requires zinc ions and high-Mr kininogen.
In a system consisting of purified proteins inositol-phospholipid-accelerated activation of prekallikrein by alpha-factor XIIa was determined by measuring the appearance of kallikrein amidolytic activity towards the chromogenic substrate, H-D-Pro-Phe-Arg-NH-PhNO2 (PhNO2, 4-nitrophenyl). The activation reaction was ionic-strength dependent. In the absence of high-Mr kininogen optimal activity was recorded at I = 50 mM. Searching for conditions, which could change this optimum towards physiological values, high-Mr kininogen was added. This resulted in an inhibition of the activity, with no change in ionic strength optimum. If, however, Zn2+ were added concomitant with high-Mr kininogen, the inhibition was abolished and optimal activity recorded at physiological ionic strength. The optimal Zn2+ concentration was found to be 0.1 mM. Kinetic analysis of the reaction demonstrated that the kcat/Km was 1.2 x 10(5) M-1 s-1 in the absence and 1.1 x 10(6) M-1 s-1 in the presence of Zn2+. Zn2+ were also required for inositol-phospholipid-accelerated initiation of the contact activation in whole plasma.
Schousboe
I
I
Department of Biochemistry C, Panum Institute, University of Copenhagen, Denmark.
D001777:Blood Coagulation / Q000502:physiology*; D002413:Cations, Divalent; D015956:Factor XIIa / Q000502:physiology*; D006801:Humans; D007294:Inositol / Q000502:physiology; D007610:Kallikreins / Q000378:metabolism; D007700:Kinetics; D007704:Kininogens / Q000502:physiology*; D009842:Oligopeptides / Q000378:metabolism; D009994:Osmolar Concentration; D010743:Phospholipids / Q000502:physiology; D011288:Prekallikrein / Q000502:physiology*; D015032:Zinc / Q000502:physiology*
D002413:Cations, Divalent; D007704:Kininogens; D009842:Oligopeptides; D010743:Phospholipids; D007294:Inositol; C026148:prolyl-phenylalanyl-arginine-4-nitroanilide; D011288:Prekallikrein; D007610:Kallikreins; D015956:Factor XIIa; D015032:Zinc