Fetuins are among the major plasma proteins, yet their biological role has remained elusive. Here we report the molecular cloning of rat fetuin and the sequence analysis of a full-length clone, RF619 of 1456 bp with an open reading frame of 1056 bp encoding 352 amino acid residues. The coding part of RF619 was identical with the cDNA sequence of the natural inhibitor of the insulin receptor tyrosine kinase from rat (pp63) except for four substitutions and a single base insertion causing divergence of the predicted protein sequences. Partial amino acid sequences of rat plasma fetuin were in agreement with the predictions based on the RF619 cDNA. Purified rat fetuin inhibited the insulin receptor tyrosine kinase in vitro. Therefore, we conclude that RF619 and pp63 cDNA encode the same protein, i.e. authentic rat fetuin which is a functional tyrosine kinase inhibitor.

To evaluate the cardiovascular actions of kinins, we established a transgenic rat line harboring the human tissue kallikrein gene, TGR(hKLK1). Under the control of the zinc-inducible metallothionein promoter, the transgene was expressed in most tissues including the heart, kidney, lung, and brain, and human kallikrein was detected in the urine of transgenic animals. Transgenic rats had a lower 24-h mean arterial pressure in comparison with control rats, which was further decreased when their diet was supplemented with zinc. The day/night rhythm of blood pressure was significantly diminished in TGR(hKLK1) animals, whereas the circadian rhythms of heart rate and locomotor activity were unaffected. Induction of cardiac hypertrophy by isoproterenol treatment revealed a marked protective effect of the kallikrein transgene because the cardiac weight of TGR(hKLK1) increased significantly less, and the expression of atrial natriuretic peptide and collagen III as markers for hypertrophy and fibrosis, respectively, were less enhanced. The specific kinin-B2 receptor antagonist, icatibant, abolished this cardioprotective effect. In conclusion, the kallikrein-kinin system is an important determinant in the regulation of blood pressure and its circadian rhythmicity. It also exerts antihypertrophic and antifibrotic actions in the heart.

A platelet-aggregating enzyme, PA-BJ, was isolated from the venom of the snake Bothrops jararaca. PA-BJ in a concentration of 3.2 x 10(-8) M promoted 95% platelet aggregation in platelet-rich plasma. SDS-polyacrylamide gel electrophoresis under reducing conditions showed a single protein band with an M(r) of 30,000. PA-BJ catalyzed the hydrolysis of several p-nitroanilide peptide substrates containing Arg or Lys at the scissile bond; among these the most sensitive were the thrombin substrates D-Phe-Pip-Arg-pNA and Tos-Gly-Pro-Arg-pNA. Both the platelet-aggregating and amidolytic activities of PA-BJ were abolished by reaction with phenylmethanesulfonyl fluoride. Several benzamidine derivatives, which are competitive inhibitors of trypsin-like serine proteinases, also inhibited the amidolytic activity of PA-BJ. Among the compounds tested, the thrombin inhibitor NAPAP [N alpha-[(2-naphthylsulfonyl)-glycyl]-4-amidinophenylalanine piperidide] showed the strongest inhibitor activity on PA-BJ. The complete amino acid sequence of PA-BJ, which, to the best of our knowledge, is the first of a platelet-aggregating enzyme from snake venom, was deduced from the N-terminal sequencing of overlapping fragments cleaved from the reduced and S-pyridylethylated protein by chemical and enzymatic methods. PA-BJ is composed of 232 amino acid residues and contains one N- and one O-glycosidically linked carbohydrate moiety at residues Asn20 and Ser23. Sequence comparison to other venom serine proteinases revealed significant homology, mainly in regions around the catalytic triad and conserved cysteine residues.

Anaphylactoid reactions (AR) are the most feared complications of hemodialysis. Recently, a high incidence of AR has been reported during dialysis with AN69 membranes in patients treated with ACE inhibitors. Plasma levels of C3a, histamine and bradykinin were measured in 12 patients at the onset of AR during dialysis with AN69. We also investigated bradykinin generation in 10 symptom-free patients dialyzed with four different membranes. None of the 12 patients studied during AR displayed excessive complement activation or histamine release. In contrast, high bradykinin plasma levels (2392 +/- 53 fmol/ml; mean +/- SEM) were observed in all nine patients of whom bradykinin was measured. One patient developed two consecutive episodes of hypersensitivity on AN69 membranes even without taking ACE inhibitors. Bradykinin levels were high in both episodes (5280 and 10467.7 fmol/ml). Furthermore, this patient showed no symptoms and normal bradykinin levels (123.4 fmol/ml) when dialyzed with other membranes. The role of the membrane type in the AR is further substantiated by the observation that AN69 also provoked a significantly higher bradykinin generation (327.6 +/- 18 fmol/ml; mean +/- SEM) during symptom-free sessions compared to other membranes like CuprophanR (5.1 +/- 7.3), HemophanR (17.2 +/- 6.3) and PolysulfoneR (39.7 +/- 6.6). Our findings strongly suggest that bradykinin is the principal mediator of AR during hemodialysis with AN69 membranes. To our knowledge it is the first time that data support the hypothesis of a more general role of bradykinin in shock-like symptoms. Furthermore, bradykinin generation must be regarded as a new marker of biocompatibility of extracorporeal treatments.

Two forms of a proteinase, KN-BJ 1 and 2, were purified to homogeneity from the venom of Bothrops jararaca. In SDS/PAGE reduced KN-BJ 1 and 2 migrated as single bands with molecular masses of 38 kDa and 39 kDa. The two enzymes have similar N-terminal amino acid sequences and specific activities on synthetic chromogenic substrates, and both release bradykinin from bovine low-molecular-mass kininogen. KN-BJ 1 and KN-BJ 2 clot fibrinogen with specific activities of 245 NIH U/mg and 219 NIH U/mg, releasing only fibrinopeptide A. The amidolytic, kinin-releasing and coagulant activities are inhibited by phenylmethylsulfonyl fluoride, demonstrating that KN-BJ is a serine proteinase. Benzamidine derivatives, which are competitive inhibitors of trypsin-like proteinases, also inhibited the amidolytic activity of KN-BJ. A cDNA clone (HS104, 2.2 kb) has been isolated from a cDNA library of B. jararaca venom glands with an ORF of 771 bp. The deduced amino acid sequence contains segments that are identical to the sequences of the N-terminus and three tryptic peptides of KN-BJ 2. Therefore, the cDNA is believed to represent the gene of KN-BJ 2. The deduced amino acid sequence indicates that KN-BJ 2 is synthesized as a prezymogen of 257 amino acids with a putative signal peptide of 18 amino acids and an activating peptide of six amino acid residues. The sequence of 233 amino acids representing the mature enzyme exhibits high similarity to sequences of serine proteinases isolated from crotalid venoms.Keywords : kinin ; kallikrein; kininogenase; Bothrops jararaca ; snake venom serine proteinase. The most characteristic physiological symptoms resultingThe presence of kinin-releasing activity in snake venom was from injection of crotalid venoms into an animal are hemor-first described by Rocha e Silva et al. (1949). The authors disrhage, lowering of the blood pressure, and disturbances of the covered that the venom of Bothrops jararaca contained a prohemostatic function (Suzuki and Iwanaga, 1970). Among the teinase that upon incubation with blood released a smooth-musvenom components, which have a wide range of physiological cle-contracting substance that produced a fall in blood pressure effects, proteinases interfering with hemostasis in vertebrates are when injected into animals and which they called bradykinin. common to crotalid and viperid snake venoms. They usually The bradykinin-releasing or kinin-releasing proteinase of B. present thrombin-like and kallikrein-like activities, which may jararaca venom has not been isolated and thoroughly characreside in different proteins (Stocker and Meier, 1988) or may be terized. It remained unclear whether the enzyme also had found as multiple activities of a single enzyme, such as crotalase intrinsic blood-coagulating activity. Holtz and Raudonat (1956) (Pirkle et al., 1981;Markland et al., 1982). All these enzymes verified that the kinin-releasing substance was precipitated by were characterized as serine proteinases and those that have ammonium sulfate with the coagulant activity. ...