The complete amino acid sequence of human antileukoprotease has been determined by direct sequencing of the inhibitory active protein isolated from seminal plasma (HUSI-I) and by sequence analysis of cDNA reverse-transcribed from mRNA prepared from cervical tissue. The inhibitor (Mr 11726) consists of 107 amino acid residues including 16 cysteines presumably forming disulfide bonds. The molecule comprises two consecutive domains which are homologous to each other, to the second domain of the basic protease inhibitor from Red Sea turtle (chelonianin) and to both domains of the whey proteins of rat and mouse. Both domains contain a pattern of cysteines known as the 'four-disulfide-core' that has also been found in wheat germ agglutinin and neurophysin.

SummaryRecently RT-PCR studies had demonstrated the expression of plasma prekallikrein (PPK) mRNA in extrahepatic tissues. The questions arose whether that is illegitimate or regular expression, and whether the mRNAs of blood coagulation factors XI and XII, and high molecular weight kininogen, components of the contact activation cascade of blood coagulation are also expressed in non-hepatic tissues. These questions were addressed in the present study by employing quantitative RT-PCR. The relative mRNA levels of the respective proteins determined in 16 human tissues indicate legitimate extrahepatic transcription of at least three of the genes. Transcription of all genes was highest in the liver, but only PPK mRNA was detected in all 16 tissues, especially high levels in pancreas, kidney, testis, spleen and prostate. We conclude from these results that PPK is synthesized in significant amounts in non-hepatic tissues and that this locally synthesized PPK may have special local functions.

Human seminal plasma contains two acid-stable proteinase inhibitors, HUSI-II (M r ~ 6 500) and HUSI-I, (M r ~ 11000) with different inhibition specificities. The inhibitory activity of HUSI-II is strongly limited to trypsin and acrosin; both enzyme-inhibitor complexes are very stable (e.g. bovine trypsin-HUSI-II complex: Kj = 1 χ 10~1 0 M; human acrosin-HUSI-II complex: K t = 2.7 χ 10~1 0 M). The inhibitor from human seminal plasma HUSI-II may therefore be seen as the natural antagonist of the sperm protease acrosin. In addition to pancreatic trypsin and α-chymotrypsin, HUSI-I forms strong complexes with neutral proteases of the lysosome-like granules from human granulocytes, for example, the elastase (K f = 2.5 χ 10~V) and cathepsin G, the chymotrypsin like protease (tf/ = 7 χ 10~8M).Remarkably, the acid-stable inhibitor from cervix uteri secretion, CUSI, and HUSI-I are also identical in their inhibition specificity.

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At present it is generally accepted that plasma prekallikrein (PPK) is synthesized in the liver and secreted into the bloodstream. Surprisingly, it has recently been shown that PPK mRNA is present also in RNA from the kidney, adrenal gland and placenta. In spite of its novelty and possible important physiological implications this finding has been neglected. Here we report that PPK mRNA is expressed also in the human brain, heart, lung,