Fibrinolysis: Its initiation and regulation

Fibrinolytic system is one of the major proteolytic pathways in vivo and primarily responsible for dissolution of thrombi. Two enzymes are primarily involved in this proteolytic system; plasminogen activator (PA) and plasmin. Plasmin is formed by a limited proteolysis of plasminogen by PA, which is mainly synthesized by and secreted from vascular endothelial cells. This proteolytic process proceeds physiologically only on the surface of fibrin. Thus, initiation and progression of the fibrinolytic process depend on the function of endothelial cells and fibrin formation. Endothelial cells may also synthesize and excrete PA inhibitor (PAI) which inhibits immediately, PA once released. The rates of synthesis and excretion of PA and PAI by endothelial cells are regulated by various factors. Among them, thrombin stimulates the release of PA whereas activated protein C may decrease the release of PAI. Thus, both enzymes enhance fibrinolytic potential. PA which has escaped from inhibition by PAI binds to fibrin. ₂-Plasmin inhibitor (₂PI) inhibits the binding of plasminogen to fibrin, thereby suppressing this fibrin-associated plasminogen activation. A part of ₂PI is cross-linked to fibrin by activated factor XIII when fibrin is formed, and the ₂PI thus cross-linked to fibrin inhibits in situ plasmin formed on fibrin. Thus, ₂PI as well as PAI plays a central role in inhibition of fibrinolysis.     

Selective expression of a probable amylase/protease inhibitor in barley aleurone cells: Comparison to the barley amylase/subtilisin inhibitor

We have cloned and sequenced a 650-nucleotide cDNA from barley (Hordeum vulgare L.) aleurone layers encoding a protein that is closely related to a known -amylase inhibitor from Indian finger millet (Eleusine coracana Gaertn.), and that has homologies to certain plant trypsin inhibitors. mRNA for this probable amylase/protease inhibitor (PAPI) is expressed primarily in aleurone tissue during late development of the grain, as compared to that for the amylase/subtilisin inhibitor, which is expressed in endosperm during the peak of storage-protein synthesis. PAPI mRNA is present at high levels in aleurone tissue of desiccated, mature grain, and in incubated aleurone layers prepared from rehydrated mature seeds. Its expression in those layers is not affected by either abscisic acid or gibberellic acid, hormones that, respectively, increase and decrease the abundance of mRNA for the amylase/subtilisin inhibitor. PAPI mRNA is almost as abundant in gibberellic acid-treated aleurone layers as that for -amylase, and PAPI protein is synthesized in that tissue at levels that are comparable to -amylase. PAPI protein is secreted from aleurone layers into the incubation medium.Abbreviations ABA abscisic acid - ASI barley amylase/subtilisin inhibitor - bp nucleotide base pairs - Da dalton - dpa days post anthesis - GA₃ gibberellic acid - PAPI probable amylase/protease inhibitor - poly(A)RNA polyadenylated RNA - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis     

Protein inhibitors of microbial proteinases from wheat,rye and triticale

Specific protein inhibitors of microbial serine proteinases were isolated from wheat (Triticum aestivum L.), rye (Secale cereale L.) and triticale using affinity chromatography on subtilisin-Sepharose 4B. The wheat inhibitor had an isoelectric point (pI) at pH 7.2, while the rye inhibitor consisted of two forms with pI values of 6.8 and 7.1. In triticale, two components were present with pIs 7.2 and 6.8. All the inhibitors had M _r values of approx. 20 000. The isolated proteins were effective inhibitors of subtilisins Carlsberg and BPN, and of fungal proteinases (EC 3.4.21.14) from the genus Aspergillus, but they were completely inactive against trypsin (EC 3.4.21.4) chymotrypsin (EC 3.4.21.1) and pancreatic elastase (EC 3.4.21.36). The inhibitors formed complexes with subtilisin in a molar ratio of 1:1. The results of chemical modifications seem to indicate that the isolated inhibitors have methionine residues in their reactive sites.Abbreviation pI isoelectric point     

Kinetics of 5-enolpyruvylshikimate-3-phosphate synthase inhibition by glyphosate

The herbicide glyphosate (N-phosphonomethyl glycine) is a potent reversible inhibitor of the 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase activity of the purified arom multienzyme complex from Neurospora crassa. Inhibition of the EPSP synthase reaction by glyphosate is competitive with respect to phosphoenolpyruvate, with K(i) 1.1 microM, and uncompetitive with respect to shikimate-3-phosphate. The kinetic patterns are consistent with a compulsory order sequential mechanism in which either PEP or glyphosate can bind to an enzyme: shikimate-3-phosphate complex.     

The experimental herbicide UKJ72J is an inhibitor of succinate oxidation in plant mitochondria

Fragments derived from human plasma fibronectin by enzymatic degradation were tested in the Boyden chamber for chemotactic activity towards various fibroblast strains. The results provide clear evidence that the chemotactic activity is restricted to a defined region of the fibronectin molecule which is the same for various fibroblast strains. The active domain is localized between the collagen binding site and the major heparin binding site, about 170 kDa apart from the N-terminal and about 70 kDa from the C-terminal ends of the two subunit peptide chains.     

Preparation of bromo[1-14C]acetyl-coenzyme A as an affinity label for acetyl-coenzyme A binding sites

Bromo[1-14C]acetyl-CoA has been prepared from CoASH and the N-hydroxysuccinimide ester of bromo[1-14C]acetic acid, and unlabeled bromoacetyl-CoA by reaction of CoASH with bromoacetyl bromide. The products were purified by high-pressure liquid chromatography. Purified bromoacetyl-CoA was characterized, and found to be a potent alkylating agent with a substantial stability in aqueous solution: it decomposed at 30 degrees C and pH 6.6 and 8.0 with halftimes of 3.3 and 2.5 h, respectively. The major breakdown products were CoASH and CoAS X CO X CH2 X SCoA. Bromo[1-14C]acetyl-CoA has been used to affinity label the acetyl-CoA binding site of 3-hydroxy-3-methylglutaryl-CoA synthase from ox liver. It was found to irreversibly inhibit the enzyme activity and bind covalently with a stoichiometry for complete inhibition of about 0.8 mol/mol enzyme dimer.     

beta-N-gamma-glutamyl diaminopropionic acid, a convulsant and an inhibitor of brain glutamate decarboxylase

The different isomers of the dipeptide beta-N-gamma-glutamyl diaminopropionate inhibit L-glutamate-1-carboxylyase (GAD, EC-4.1.1.15) activity in mouse brain homogenates. The L-D isomer is the most effective as an inhibitor, while the D-D isomer is least inhibitory. The different isomers are neurotoxic to mice and the chick, the L-D isomer being the most toxic. The neurotoxicity of the isomers in mice was also associated with a significant lowering in GAD activity in the brains of convulsing mice.     

Caprolactam,a light-promoted growth inhibitor in sunflower seedlings

A neutral growth inhibitor, isolated from methanolic extracts of sunflower seedlings, was characterized by spectral data as caprolactam. Light-grown se     

The effect of various inhibitors of DNA synthesis on the repair of DNA photoproducts

The effect on DNA repair of several inhibitors of DNA synthesis has been investigated in CHO cells. Three assays were employed following ultraviolet irradiation of G₁ cells: unscheduled DNA synthesis, removal of antibody binding sites and alkaline elution. Cytosine arabinoside and aphidicolin were found to reduce unscheduled DNA synthesis in a dose-dependent manner without affecting the removal of antibody-binding sites. Strand rejoining was also inhibited. These results are consistent with the hypothesis that inhibition is due to premature chain termination during repair synthesis some time after excision of the lesion. Conversely, inhibition of unscheduled DNA synthesis by novobiocin is paralleled by inhibition of excision of the lesion. However, no inhibition of incision was apparent. Since nalidixic acid, an inhibitor of topoisomerase II, did not inhibit excision, it is unlikely that the primary site of action of novobiocin is this topoisomerase. The possibility that a second topoisomerase and/or a polymerase are affected is discussed in the light of previously published data.     

Secondary structure features of ribosomal RNA species within intact ribosomal subunits and efficiency of RNA-protein interactions in thermoacidophilic (Caldariella acidophila,Bacillus acidocaldarius) and mesophilic (Escherichia coli) bacteria

Ribosomal subunits of Caldariella acidophila (max.growth temp., 90°C) have been compared to subunits of Bacillus acidocaldarius (max. growth temp., 70°C) and Escherichia coli (max. growth temp., 47°C) with respect to (a) bihelical content of rRNA; (b) G·C content of bihelical domains and (c) tightness of rRNA-protein interactions. The principal results are as follows. 1. Subunits of C. acidophila ribosomes (T_m = 90–93°C) exhibit considerable thermal tolerance over their B. acidocaldarius (T_m = 77°C) and E. coli counterparts (T_m = 72°C). 2. Based on the ‘melting’ hyperchromicities of the intact ribosomal subunits a 51–55% fraction of the nucleotides appears to participate in hydrogen-bonded base pairing regardless of ribosome source, whereas a larger fraction, 67–70%, appears to be involved in hydrogen bonding in the naked rRNA species. 3. The G·C content of bihelical domains of both free and ribosome-bound rRNA increases with increasing thermophily; based on hyperchromicity dispersion spectra of intact subunits and free rRNA, the bihelical parts of C. acidophila rRNA are estimated to contain 63–64% G·C, compared to 58.5% G·C for B. acidocaldarius and 55% G·C for E. coli. 4. The increment in ribosome T_m values with increasing thermophily is greater than the increase in T_m for the free rRNA, indicating that within ribosomes bihelical domains of the thermophile rRNA species are stabilized more efficiently than their mesophile counterparts by proteins or/ and other component(s). 5. The efficiency of the rRNA-protein interactions in the mesophile and thermophile ribosomes has been probed by comparing the releases, with LiCl-urea, of the rRNA species from the corresponding ribosomal subunits stuck to a Celite column through their protein moiety; it has been established that the release of C. acidophila rRNA from the Celite-bound ribosomes occurs at salt-urea concentrations about 4-fold higher than those required to release rRNA from Celite-bound E. coli ribosomes. 6. Compared to E. coli, the C. acidophila 50 and 30 S ribosomal subunits are considerably less susceptible to treatment designed to promote ribosome unfolding through depletion of magnesium ions.