Determination of prekallikrein in human plasma: optimal conditions for activating prekallikrein.

A method for the assay of human plasma prekallikrein in which a chromogenic synthetic tripeptide, PPAN, is used as a substrate for kallikrein is described. The conversion of prekallikrein to kallikrein is achieved by cold activation (0 degrees C) with water-soluble dextran sulfate. Conditions for obtaining optimal amounts of free kallikrein with respect to concentration of dextran sulfate, activation time, inhibitors (C-1-inactivator), and requirement of factor XII have been determined. The activation procedure is compared to other known procedures. The assay system was worked out for pooled normal plasma and is applicable to any plasma sample not liable to unwanted preactivation or incomplete inactivation, as revealed by control experiments. A survey in 15 apparently health individuals showed a mean activity of 476 +/- 58 (S.D.) mU/ml with a range of 385 to 586 mU/ml.