Adenylate cyclase activity in cyanobacteria: activation by Ca(2+)-calmodulin and a calmodulin-like activity

An adenylate cyclase activity was partially characterized in the cyanobacterium Anabaena sp. The enzyme activity is found in soluble cell fractions and shows an apparent molecular weight of about 183,400. This adenylate cyclase is activated by Ca2+ and bovine brain or spinach calmodulin and it is inhibited by EGTA and some phenothiazine derivatives. Furthermore, Anabaena sp. extracts contain a calmodulin-like activity which stimulates bovine brain cyclic AMP phosphodiesterase and the Anabaena adenylate cyclase. EGTA and phenothiazine derivatives block the cyanobacterial modulator effect.     

The helminth fauna of CHIle: IV. Nematodes of the genera Anisakis Dujardin, 1845 AND Phocanema Myers, 1954 in relation with gastric ulcers in a South American Sea Lion, Otaria byronia

A gastric ulcer was diagnosed in a South American Sea Lion, Otario byronia, captured along the northern coast of Chile. Species of Anisakis and Phocanema were found to be associated with the lesions. A discussion of the histopathologic damage observed is presented, along with probable etiology of the ulcer.     

Regulation of uracil uptake in Escherichia coli by adenosine 3',5'-monophosphate.

Culture of a wild-type strain of Escherichia coli in the presence of cyclic AMP leads to an impairment of uracil uptake. Half maximum inhibition of uracil uptake was observed at 1.5 mM cyclic AMP. The effect seems to be specific since no inhibition was found in cultures supplemented with ATP, ADP or 5'-AMP. Similarly the inhibition was not observed in cultures of a mutant deficient in the cyclic AMP receptor protein. The inhibition in uracil uptake, found in bacteria cultured in the presence of cyclic AMP, is not a consequence of a reduction in the growth rate. On the other hand, this inhibition was observed only in cultures containing glucose or pyruvate as carbon source.     

Heterodimer formation between superoxide dismutase and its copper chaperone

Copper, zinc superoxide dismutase (SOD1) is activated in vivo by the copper chaperone for superoxide dismutase (CCS). The molecular mechanisms by which CCS recognizes and docks with SOD1 for metal ion insertion are not well understood. Two models for the oligomerization state during copper transfer have been proposed: a heterodimer comprising one monomer of CCS and one monomer of SOD1 and a dimer of dimers involving interactions between the two homodimers. We have investigated protein-protein complex formation between copper-loaded and apo yeast CCS (yCCS) and yeast SOD1 for both wild-type SOD1 (wtSOD1) and a mutant SOD1 in which copper ligand His 48 has been replaced with phenylalanine (H48F-SOD1). According to gel filtration chromatography, dynamic light scattering, analytical ultracentrifugation, and chemical cross-linking experiments, yCCS and this mutant SOD1 form a complex with the correct molecular mass for a heterodimer. No higher order oligomers were detected. Heterodimer formation is facilitated by the presence of zinc but does not depend on copper loading of yCCS. The complex formed with H48F-SOD1 is more stable than that formed with wtSOD1, suggesting that the latter is a more transient species. Notably, heterodimer formation between copper-loaded yCCS and wtSOD1 is accompanied by SOD1 activation only in the presence of zinc. These findings, taken together with structural, biochemical, and genetic studies, strongly suggest that in vivo copper loading of yeast SOD1 occurs via a heterodimeric intermediate.     

Mechanistic studies of the yeast polyamine oxidase Fms1: kinetic mechanism, substrate specificity, and pH dependence

The flavoprotein oxidase Fms1 from Saccharomyces cerevisiae catalyzes the oxidation of spermine and N(1)-acetylspermine to yield spermidine and 3-aminopropanal or N-acetyl-3-aminopropanal. The kinetic mechanism of the enzyme has been determined with both substrates. The initial velocity patterns are ping-pong, consistent with reduction being kinetically irreversible. Reduction of Fms1 by either substrate is biphasic. The rate constant for the rapid phase varies with the substrate concentration, with limiting rates for reduction of the enzyme of 126 and 1410 s(-1) and apparent K(d) values of 24.3 and 484 μM for spermine and N(1)-acetylspermine, respectively. The rapid phase is followed by a concentration-independent phase that is slower than turnover. The reaction of the reduced enzyme with oxygen is monophasic, with a rate constant of 402 mM(-1) s(-1) with spermine at 25 °C and 204 mM(-1) s(-1) with N(1)-acetylspermine at 4 °C and pH 9.0. This step is followed by rate-limiting product dissociation. The k(cat)/K(amine)-pH profiles are bell-shaped, with an average pK(a) value of 9.3 with spermine and pK(a) values of 8.3 and 9.6 with N(1)-acetylspermine. Both profiles are consistent with the active forms of substrates having two charged nitrogens. The pH profiles for the rate constant for flavin reduction show pK(a) values of 8.3 and 7.2 for spermine and N(1)-acetylspermine, respectively, for groups that must be unprotonated; these pK(a) values are assigned to the substrate N4. The k(cat)/K(O(2))-pH profiles show pK(a) values of 7.5 for spermine and 6.8 for N(1)-acetylspermine. With both substrates, the k(cat) value decreases when a single residue is protonated.     

Structural analysis of the N‐terminal fragment of the antiangiogenic protein endostatin: A molecular dynamics study

Endostatin is a potent antiangiogenic protein derived from the noncollagenous domain 1 (NC1) of collagen XVIII. The mechanism by which endostatin exerts its antiangiogenic effect is still incompletely understood. It has been shown that the 27 amino acid N‐terminal fragment of murine endostatin has antitumor, antimigration, and antipermeability activities comparable to the full soluble protein. To understand how this peptide can exert such elaborate function, we performed structural analysis using molecular dynamics to evaluate the behavior of this fragment in aqueous environment. Here, we show that the N‐terminal peptide of murine endostatin is able to assume a well‐defined structure, folding into a zinc‐dependent β‐hairpin conformation. Analyzing the folding mechanism, we were able to understand why the N‐terminal peptide of human endostatin with the same length failed to acquire a stable conformation. Conversely, we were able to predict the successful folding of the R4Q mutant and of a shorter form of the human peptide with 25 residues. Finally, we show that the β‐hairpin conformation assumed by the zinc‐bound peptide of murine endostatin has a high structural similarity with fragments of another family of angiogenesis inhibitors: the integrin‐binding portion of the NC1 domain of collagen IV. Indeed, our docking simulations show that arresten, canstatin, and the endostatin peptide bind to the same spot of αVβ3 integrin, suggesting similar interactions via a common binding site on this receptor. Proteins 2011;. © 2011 Wiley‐Liss, Inc.     

Nerve Growth Factor Effect on Adenosine Transport in Cultured Chromaffin Cells

Chromaffin cells both recently isolated or in culture present a high-affinity adenosine transporter with a Km value of 1 microM. When cells were exposed to nerve growth factor (NGF; 10 ng/ml), the adenosine transporter affinity decreased to 3 microM. This value was maintained from 3 days after plating to the end of the culture period. A change in the transport capacity was observed, with a significant increase (approximately 200-260%) in NGF-cultured cells throughout the period studied.