Henrique P. B. Magalhães

Coagulant thrombin-like enzymes from the venoms of Brazilian and Peruvian bushmaster (Lachesis muta muta) snakes.

Two isoforms of a thrombin-like enzyme designated TLE-B and TLE-P were purified from the venoms of Lachesis muta muta (bushmaster) snakes captured in two different geographical localities, Manaus (Brazil) and Pucallpa (Perú). TLE-B and TLE-P showed Mr values of 44000 and 43000 under reducing conditions on SDS-PAGE, which decreased to 27000 after deglycosylation with N-glycosidase F (PNGase F). The purified proteinases split off fibrinopeptide A rapidly from human fibrinogen and fibrinopeptide B more slowly. In addition, both enzymes released the N-terminal peptide (Mr=4572) containing the first 42 residues from the Bbeta-chain. Their specific clotting activities were equivalent to 1000 and 900 NIH thrombin units/mg on human fibrinogen and 526 and 606 NIH thrombin units/mg on bovine fibrinogen for TLE-B and TLE-P, respectively. Kinetic properties of these enzymes were determined using representative chromogenic substrates. Tryptic peptide mapping of the two native enzymes suggested a large degree of structural similarity. Purified rabbit IgG against TLE-B reacted with both enzymes forming a continuous precipitin line on immunodiffusion. Furthermore, Western blot and indirect ELISA were used to compare the antigenic cross-reactivity for both enzymes as well as the venoms of L. muta muta and Bothrops snakes. Incubation of human alpha2-macroglobulin (alpha2-M) with each enzyme at molar ratios of 1:1, 1:2 and 1:4 enzyme:inhibitor resulted in retarding their clotting activities by approximately 12 times, whereas their amidolytic activities were not affected. However, the Mr 180000 subunits of alpha2-M were not cleaved by these enzymes, suggesting that alpha2-M inhibits TLEs by steric hindrance. Similarly, inhibitions of their clotting activities were obtained using high concentrations of rabbit IgG (40 microg, corresponding to molar ratio enzyme:inhibitor of 1:2) against TLE-B.

Thrombin-like enzyme from Lachesis muta muta venom: isolation and topographical analysis of its active site structure by means of the binding of amidines and guanidines as competitive inhibitors

A serine protease enzyme was purified from Lachesis muta muta venom, with 40% yield, by gel filtration on Sephadex G-100 and affinity chromatography on Sepharose-agmatin. Homogeneity of the enzyme preparation was demonstrated by sodium dodecyl sulfate polyacrylamide gel electrophoresis and the enzyme had a relative mol. wt of 45,000. The molar extinction coefficient at 280 nm was 62,127 (M x cm)-1. The enzyme hydrolysed Bz-Arg-Nan with Ks = 0.233 +/- 0.08 mM and kcat = 2.80 +/- 0.07 sec-1. All the amidines and guanidines tested for their inhibitory effect on thrombin-like enzyme behaved as competitive inhibitors of the enzyme with Ki values in the range 6.2 microM to 42.3 mM for amidines and 0.19 mM to 9.31 mM for guanidines. Dissociation constant values were analyzed in terms of the binding of the inhibitors with the subsite S1, the specificity pocket of the enzyme, Ki values were discussed in accordance with those for trypsin inhibition. beta-Naphthamidine was the strongest inhibitor, while guanidine was the weakest. The differences among the Ki values were interpreted in terms of the shape of the enzyme active site. For meta- and para-substituted benzamidinium ions a good correlation was found between log l/Ki and sigma Hammett values of the substituents. The substituent effects in the pi-electrons of the benzamidine ring were considered in the frame of Hückel molecular orbital theory. A model for the binding of p-benzamidine derivatives with the primary specificity S1 subsite of the enzyme active site was proposed.

Kinetic Characterization of Leucurobin, a Coagulant Thrombin-Like Enzyme from the Venom of Bothrops leucurus~!2009-03-01~!2010-04-16~!2010-06-11~!

In the present study, the kinetic characterization of leucurobin, a thrombin-like enzyme isolated from the venom of Bothrops leucurus was evaluated. This serpent is very common in the northeast of Brazil, but little is known about its venom. Leucurobin showed amidase activity against chromogenic substrates of the peptidyl-pNA type containing an Arg residue at P1. D-Phe-Pro-Arg-pNA was observed to be the best substrate of those tested. The amidase activity of leucurobin with this substrate was strongly inhibited by sodium and potassium ions and was weakly inhibited by calcium and magnesium ions. Leucurobin presented a high coagulating activity in vitro with citrated human plasma and with purified bovine fibrinogen. The coagulating activity with fibrinogen was inhibited by the presence of sodium and potassium ions, but not by calcium or magnesium ions. No interference in the amidase and coagulating activities by the glycoside fraction of native leucurobin was observed. The S1 site was found to be anionic, and the S2 and S3 sites are hydrophobic.

Creatinine and cytokines plasma levels related to HLA compatibility in kidney transplant patients

Introduction:The success of kidney transplantation depends on prevention of organ rejection by the recipient’s immune system, which recognizes alloantigens present in transplanted tissue. Human leukocyte antigen (HLA) typing is one of the tests used in pre-renal transplantation and represents one of the most important factors for a successful procedure.Objective:The present study evaluated creatinine and cytokines plasma levels in kidney transplant patients according to pre-transplant HLA typing.Methods:We assessed 40 renal transplanted patients selected in two transplant centers in Belo Horizonte (MG).Results:Patients were distributed into three groups according to HLA compatibility and, through statistical analysis, the group with more than three matches (H3) was found to have significantly lower post-transplant creatinine levels, compared to groups with three or fewer matches (H2 and H1, respectively). The median plasma levels of cytokines interleukin 6 (IL-6), tumor necrosis factor alpha (TNF-α), and interleukin 10 (IL-10) were evaluated according to the number of matches. Pro-inflammatory cytokines (IL-6 and TNF-α) were significantly higher in groups with lower HLA compatibility. On the other hand, the regulatory cytokine IL-10 had significantly higher plasma levels in the group with greater compatibility between donor and recipient.Conclusion:These findings allow us to infer that pre-transplant HLA typing of donors and recipients can influence post-transplant renal graft function and may contribute to the development and choice of new treatment strategies.

Effectiveness to identify acute myocardial infarction using the Manchester screening in patients with chest pain at the emergency service

Among cardiovascular diseases (CVD), acute coronary syndrome (ACS) is the main manifestation, corresponding to signs and symptoms that occur with ischemia and outcome of angina or acute myocardial infarction (AMI). The aim of this study was to investigate the performance of biochemical markers eligible in a chest pain protocol, using Point of care Test (POCT), in patients in a reference emergency room.