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Incubation of human citrated plasma with dextran sulphate at 0°C was found to generate kallikrein activity as determined with the chromogenic synthetic tripeptide α-N-Bz-Pro-Phe-Arg-p. nitroanilide (0.16 mM). The possible use of the synthetic soluble dextran sulphate (MW 500,000) instead of the commonly used insoluble kaolin for activating the plasma kallikrein system was explored. The rate of activation of prekallikrein to kallikrein was dependent on: a) the concentration of dextran sulphate until a plateau was reached at 12.5 μg/ml; and b) the concentration of factor XII in the entire range up to 100%, as varied by mixing deficient and normal plasma. Activation was only slightly influenced by increased levels of C1-inactivator. In comparing dextran sulphate with kaolin, it was noticed that activation by means of dextran sulphate was slower (optimum at 7 and 2 min, respectively) and could be stopped by dilution. With kaolin (or glass), the activation continued even at high dilution (1:162) in the cuvet, preventing a proper study of the activation process. Dextran sulphate also did not interfere with the spectrophoto-metric assay, in contrast to the light-scattering properties of the insoluble kaolin. Optimum conversion of prekallikrein to kallikrein is reached in normal pooled plasma in 7 min at 0°C with 25 μg/ml dextran sulphate. The same is true for other plasma samples, if not liable to unwanted preactivation or incomplete activation, as revealed by control experiments. In 15 apparently healthy individuals, a mean activity of 476 ± 58 (SD) mU/ml was found. It is concluded that dextran sulphate can be used advantageously in the assay of prekallikrein activation and prekallikrein levels.

Assay for Prekallikrein Levels and Prekallikrein Activation in Human Plasma Using Dextran Sulphate as a Soluble Activator