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The plasmas of 18 species were assayed for Fletcher factor activity using human Fletcher trait plasma as a substrate. Ape, swine, guinea pig and mouse plasmas had Fletcher factor activity comparable to that of human plasma. In contrast, bovine, dog, cat, rabbit and cetacean plasmas contained almost no Fletcher factor. In immunodiffusion studies using rabbit anti-human kallikrein (Fletcher factor) serum, only human and ape plasmas gave a precipitin line. There is a good correlation between Fletcher factor activity tested on human substrates and kaolin-activated TAMe esterase levels of each species' own plasma at 1 min incubation.
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Saito et al. (1974) studied this question.
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