Identification of guanine and adenine nucleotides as activators of glucose-1,6-bisphosphatase activity from rat skeletal muscle.

Glucose-1,6-bisphosphatase activity in rat skeletal muscle extracts was lost after exhaustive dialysis or precipitation with ammonium sulfate. Most of the original activity was recovered when the boiled extract was added to the ammonium sulfate precipitate. Qualitative analysis of the boiled extract revealed that the activator was either a nucleoside or a nucleotide. The results show that at concentrations between 0.05 and 1 mM, only guanine and adenosine derivatives are effective as activators, the former being more powerful. However, only guanosine, ADP, and AMP have an activating effect at the concentrations found in the boiled extract. The results of assays in vitro suggest that adenine nucleotides could be physiological modulators of glucose-1,6-bisphosphatase activity during muscle contraction.     

Metabolism of glycerate 2,3-P2--XII. Characterization of the 2,3-bisphosphoglycerate synthase-phosphatase and of the hybrid phosphoglycerate mutase/2,3-bisphosphoglycerate synthase-phosphatase from pig brain

2,3-Bisphosphoglycerate synthase-phosphatase and the hybrid phosphoglycerate mutase/2,3-bisphosphoglycerate synthase-phosphatase have been partially purified from pig brain. Their 2,3-bisphosphoglycerate synthase, 2,3-bisphosphoglycerate phosphatase and phosphoglycerate mutase activities are concurrently lost upon heating and treatment with reagents specific for histidyl, arginyl and lysyl residues. The two enzymes differ in their thermal stability and sensitivity to tetrathionate. Substrates and cofactors protect against inactivation, the protective effects varying with the modifying reagent. The synthase activity of both enzymes shows a nonhyperbolic pattern which fits to a second degree polynomial. The Km, Ki and optimum pH values are similar to those of the 2,3-bisphosphoglycerate synthase-phosphatase from erythrocytes and the hybrid enzyme from skeletal muscle. The synthase activity is inhibited by inorganic phosphate and it is stimulated by glycolyate 2-P.     

Phylogeny and ontogeny of the phosphoglycerate mutases.--V. Inactivation of phosphoglycerate mutase isozymes by histidine-specific reagents

1. The three isozymes of glycerate-2,3-P2 dependent phosphoglycerate mutase present in tissues of mammals and reptiles were inactivated by both treatment with diethylpyrocarbonate and photooxidation with rose bengal. 2. Inactivation of type M isozyme purified from rabbit muscle was complete when two histidine residues per enzyme subunit were carboethoxylated. Hydroxylamine removed the carboethoxy groups, with partial recovery of the enzymatic activity. The cofactor protected the enzyme against inactivation. 3. The inactivation of rabbit muscle phosphoglycerate mutase by photooxidation with methylene blue and rose bengal was sharply pH dependent. The pH profile of enzyme inactivation followed the titration curve of histidine, suggesting that this amino acid was critical for enzyme activity. Glycerate-2,3-P2 did not protect phosphoglycerate mutase against photoinactivation.     

Metabolism of glucose 1,6-P2--III. Partial purification and characterization of glucose 1,6-P2 synthase from pig skeletal muscle

1. Glycerate 1,3-P2-dependent glucose, 1,6-P2 synthase has been purified 2000-fold from pig skeletal muscle, with a yield of 75%. 2. The enzyme possesses fructose 1,6-P2-dependent glucose 1,6-P2 synthase and phosphoglucomutase activities, which represent 0.1 and 60% of the main activity, respectively. 3. Both glucose 1-P and glucose 6-P can act as acceptors of the phosphoryl group from glycerate 1,3-P2. 4. The Km values are 19 microM and 67 nM for glucose 1-P and glycerate 1,3-P2, respectively. 5. The enzyme is inhibited by glycerate 2,3-P2, fructose 1,6-P2, glycerate 3-P, phosphoenolpyruvate and lithium, the inhibition pattern varying with the compound.     

Vanadate increases oxygen affinity and affects enzyme activities and membrane properties of erythrocytes

Incubation of blood with vanadate markedly increases the affinity of hemoglobin for oxygen, decreases the deformability of erythrocytes, reduces their osmotic fragility and alters their morphology, determining the appearance of equinocytic forms. Since vanadate is easily taken up by the erythrocytes and binds hemoglobin, these effects might result from interactions of vanadate with hemoglobin and with membrane proteins at the glycerate-2, 3-P₂ and/or ATP binding site. In addition, vanadate inhibits phosphoglycerate mutase, phosphoglucomutase and adenylate-kinase activities from hemolysates, suggesting a possible inhibitory effect on erythrocyte metabolism     

Simvastatin and atorvastatin enhance gene expression of collagen type 1 and osteocalcin in primary human osteoblasts and MG-63 cultures

To clarify the mechanism of the stimulatory effect of statins on bone formation, we have assessed the effect of simvastatin and atorvastatin on osteoblast activity by analysing cell proliferation, as well as collagen, osteocalcin, and bone morphogenetic protein-2 (BMP2) gene expression in primary human osteoblast (hOB) and MG-63 cell line cultures. Explants of bone from patients without any metabolic disease under orthopedic hip procedures were used to obtain hOB. Cell cultures were established, synchronized, and different concentrations of simvastatin or atorvastatin were added (10(-9) M, 10(-8) M, 10(-7) M, 10(-6) M) during the experiment. Cell proliferation was analyzed after 24 h. Collagen polypeptide alpha1 type 1 (COL1A1) gene expression, osteocalcin, and BMP2 expression levels were quantified by real-time PCR after 24 h incubation with statins. There was a statistically significant decrease in cell proliferation related to simvastatin or atorvastatin addition at all concentrations in primary hOB compared with those not treated. A significant increase in COL1A1, osteocalcin, and BMP2 gene expression was detected when hOB cultures were treated with simvastatin or atorvastatin at different concentrations. Similar but less significant effects were found on MG-63 cells. After statin treatment we observed both an arrest of proliferation in hOB cells and an increase in collagen, osteocalcin, and BMP2 gene expression, consistent with a stimulatory effect towards mature osteoblast differentiation. These findings support the bone-forming effect of statins, probably through the BMP2 pathway.     

Catheter ablation of atrial incisional tachycardia mistaken for atrial flutter

Incisional sustained tachycardias are frequent in patients who have undergone a surgical repair of interatrial defect. A 43-year-old woman with drug refractory, highly symptomatic, persistent atrial tachycardia in the last year, was referred to our unit for catheter ablation. The patient had undergone a cardiac operation for repairing interatrial secundum ostium type defect with a patch five years before. A previous radiofrequency ablation procedure had been performed for common atrial flutter. We describe a case of incisional atrial tachycardia ablation guided by the new EnSite NavX system equipped with a new electroanatomic mapping system.     

Topography studies on the membrane interaction mechanism of the eosinophil cationic protein

The eosinophil cationic protein (ECP) is an antipathogen protein involved in the host defense system. ECP displays bactericidal and membrane lytic capacities [Carreras et al. (2003) Biochemistry 42, 6636-6644]. We have now characterized in detail the protein-membrane interaction process. All observed fluorescent parameters of the wild type and single-tryptophan-containing mutants, as well as the results of decomposition analysis of protein fluorescence, suggest that W10 and W35 belong to two distinct spectral classes I and III, respectively. Tryptophan residues were classified and assigned to distinct structural classes using statistical approaches based on the analysis of tryptophan microenvironment structural properties. W10 belongs to class I and is buried in a relative nonpolar, nonflexible protein environment, while W35 (class III) is fully exposed to free water molecules. Tryptophan solvent exposure and the depth of the protein insertion in the lipid bilayer were monitored by the degree of protein fluorescence quenching by KI and brominated phospholipids, respectively. Results indicate that W35 partially inserts into the lipid bilayer, whereas W10 does not. Further analysis by electron microscopy and dynamic light scattering indicates that ECP can destabilize and trigger lipid vesicle aggregation at a nanomolar concentration range, corresponding to about 1:1000 protein/lipid ratio. No significant leakage of the vesicle aqueous content takes place below that protein concentration threshold. The data are consistent with a membrane destabilization "carpet-like" mechanism.     

Cytologic diagnosis of ocular melanocytoma: a case report

BACKGROUND: Pigmented lesions of the eye represent a challenging field from both clinical and pathologic approaches. The importance of a correct diagnosis in this case is enhanced by the delicate structures involved and their difficult accessibility. CASE: We report a case of a 51-year-old man with acute vision loss and the feeling of a foreign body in the left eye diagnosed with vitreous hemorrhage. A small, pigmented lesion in the proximity of optic nerve head was detected. After a 9-year follow-up, a definitive diagnosis of melanocytoma was achieved in vitrectomy cytology. Smears showed a population of plump, cohesive melanocytes and elongated cells with cytoplasmic melanin and uniform rounded nuclei. No change in the lesion has occurred 3 years after vitrectomy. CONCLUSION: Fine needle aspiration proved to be helpful and reliable for the correct diagnosis of melanocytoma, which does not require additional treatment.