Practical application of the protein C activator Protac from Agkistrodon contortrix venom

The protein C activator Protac from A. contortrix venom is being investigated as a potential antithrombotic agent and as a tool for the preparation of activated protein C. Its established major application is the zymogen activation in functional protein C determinations based on either a clotting assay or a chromogenic substrate technique. The sensitivity of the activated partial thromboplastin time as an indicator reaction for Protac activated protein C depends on the contact activator component of the reagent. Protein C dose-response increased in the following order: kaolin greater than ellagic acid greater than sulfatide. This phenomenon is due to a competition of molecular affinities between Protac, plasma components and the different activating surfaces.     

Reduction of tumor growth following treatment with a glutamine antimetabolite

Assessment of arterial-venous differences across transplanted methylcholanthrene-induced sarcomas in rats revealed significant decreases in plasma concentrations of glutamine, serine and glucose. Treatment with the glutamine antimetabolite, acivicin, significantly reduced tumor weights by 65% at the conclusion of the experiment 34 days after tumor induction. These results suggest that glutamine is an essential metabolic substrate for tumor growth and that blockade of glutamine utilization can inhibit the growth of these transplantable sarcomas.     

Human neutrophil response to recombinant neisserial Opa proteins

Interactions of human neutrophils with recombinant Escherichia coli expressing gonococcal outer membrane Opa proteins were examined using chemiluminescent and biological assays. Seven opa loci from Neisseria gonorrhoeae MS11 4.8 were expressed as beta-lactamase-Opa fusion proteins that contained all but the mature N-terminal amino acid of the full-length Opa protein fused to three N-terminal amino acids derived from the mature beta-lactamase. The Opa fusion proteins were exported and assembled in the outer membrane of E. coli in a manner similar to that of Opa in N. gonorrhoeae, as evaluated by antibody binding and in situ proteolytic cleavage. All fusion proteins exhibited the characteristic heat-modifiable migration in SDS-polyacrylamide gel electrophoresis that typifies Opa proteins of neisseriae. Opa fusion proteins conferred on E. coli the ability to stimulate a chemiluminescent response from human neutrophils in the absence of antibody or complement. The nature of the response in terms of chemiluminescence, phagocytosis, and killing was in all cases analogous to that seen using N. gonorrhoeae expressing the equivalent Opa protein. Neither E. coli nor gonococci expressing OpaA elicited a response from neutrophils. Use of E. coli expressing Opa fusions should be useful in defining their biological activities and pathogenic roles.     

Mechanistic studies of lanosterol C-32 demethylation. Conditions which promote oxysterol intermediate accumulation during the demethylation process

Conditions have been established which promote the accumulation of the dihydrolanosterol C-32 demethylation intermediates lanost-8-en-3 beta,32-diol and 3 beta-hydroxylanost-8-en-32-aldehyde with intact hepatic microsomes. Accumulation of dihydrolanosterol-derived oxysterols occurs with a variety of assay manipulations which include short incubation times, limiting enzyme amounts, high pH, and increasing substrate concentration. In addition, competitive inhibition of dihydrolanosterol demethylation by lanosterol, or the reciprocal inhibition of lanosterol demethylation by dihydrolanosterol, leads to oxysterol accumulation at the expense of demethylated end product. Similarly, the nonsteroidal demethylase inhibitors miconazole and ketoconazole promote oxysterol accumulation in a concentration-dependent manner. Finally, cholesterol loading of isolated microsomes results in changes in the measured kinetic constants, Km and Vmax, and results in enhanced oxysterol accumulation above that seen in control microsomal preparations. The major oxysterol intermediate accumulated under all the conditions described above is the C-32 aldehyde in an approximate 3:1 ratio to the C-32 alcohol. These data support the conclusion that a single enzyme species is responsible for all three oxidations of the C-32 demethylation sequence. In addition, intermediates which do not routinely accumulate during demethylation are freely diffusible from the enzyme when appropriate conditions are established to prevent their further metabolism.     

The early effect of sublethal X-irradiation of phagocytic cells in mouse blood and the influence of cystamine as measured by chemiluminescence

The metabolic burst accompanying phagocytosis of granulocytes (PMN) leads to the generation of activated oxygen species such as O-2, H2O2, 1O2 and OH; which give rise to chemiluminescence (CL) in the presence of luminol. Reliable CL-measurements of stimulated PMN can be carried out in freshly drawn mouse blood, when photon counts are related to the number of PMN. Effects of low dose total body X-irradiation were studied using C57B1/6 mice. It was found that 24 and 48 hours after irradiation (0.24-0.95 Gy) CL of whole blood was slightly decreased. If however CL-counts were related to the number of PMN, an enhanced CL per single granulocyte was recorded. The administration of cystamine leads to an immune stimulating effect of unirradiated animals. In animals, who received 0.95 Gy a distinct radioprotective effect of cystamine can be observed.     

Ion-specific diffusion rates through transmembrane protein channels. A molecular dynamics study

The migration of different alkali metal cations through a transmembrane model channel is simulated by means of the molecular dynamics technique. The parameters of the model are chosen in close relation to the gramicidin A channel. Coulomb- and van der Waals-type potentials between the ions and flexible carbonyl groups of the pore-forming molecule are used to describe the ion channel interaction. The diffusion properties of the ions are obtained from three-dimensional trajectory calculations. The diffusion rates for the different ions Li+, Na+, K+ and Rb+ are affected not only by the mass of the particles but also very strongly by their size. The latter effect is more pronounced for rigid channels, i.e., for binding vibrational frequencies of the CO groups with v greater than 400 cm-1. In this range the selectivity sequence for the diffusion rates is the inverse of that expected from normal rate theory but agrees with that found in experiments for gramicidin A.