Assay of procarboxypeptidase U, a novel determinant of the fibrinolytic cascade, in human plasma.
BACKGROUND
Procarboxypeptidase U (proCPU) is a novel proenzyme found in human plasma. The active form, carboxypeptidase U (CPU; EC 3.4.17.20), retards the rate of fibrinolysis through its ability to cleave C-terminal lysine residues on fibrin partially degraded by plasmin. This reduces the number of high-affinity plasminogen-binding sites on fibrin.


METHODS
We developed an assay to determine the proCPU concentration in human plasma. The assay involved quantitative conversion of proCPU to active CPU by thrombin-thrombomodulin, a very efficient activator of proCPU, followed by determination of the enzymatic activity of CPU with the substrate hippuryl-L-arginine, using an HPLC-assisted determination of the released hippuric acid. Using this method, we established a reference interval based on 490 healthy individuals.


RESULTS
The mean proCPU concentration, determined after activation of the zymogen in diluted plasma and expressed as CPU activity, was 964 U/L, with a SD of 155 U/L. The population showed a gaussian distribution. However, we noticed important differences related to age and the use of hormone preparations.


CONCLUSIONS
The sensitivity and precision of the method make it suitable for routine clinical determinations and as a reference procedure.
Schatteman
K A
KA
Department of Clinical Biochemistry, University of Antwerp, Universiteitsplein 1, B-2610 Wilrijk, Belgium.
Goossens
F J
FJ
Scharpé
S S
SS
Neels
H M
HM
Hendriks
D F
DF
D000328:Adult; D000368:Aged; D025901:Carboxypeptidase B2; D002268:Carboxypeptidases / Q000097:blood*; D002851:Chromatography, High Pressure Liquid; D004789:Enzyme Activation; D005260:Female; D005342:Fibrinolysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013917:Thrombin; D018180:Thrombomodulin
D018180:Thrombomodulin; D002268:Carboxypeptidases; D025901:Carboxypeptidase B2; D013917:Thrombin