Glycogen phosphorylase activity of full term immature human placentas]

Human placenta contains glycogen phosphorylase activity (E.C. 2.4.1.1) in two interconvertible forms, one is already active and the other is actibatable by 5' AMP. The human placenta contains also a sufficient amount of endogenous phosphorylase b kinase and phosphorylase a phosphatase, to allow this interconversion. The phosphorylase activity is higher in immature placentas than in full-term organs, as in the latter the inactive phosphorylase is only partially revealed by 5' AMP as in other steroidogenic organs. By contrast, in immature placentas the inactive glycogen phosphorylase is completely revealed by this nucleotide.     

Control of adenine nucleotide metabolism and glycolysis in vertebrate skeletal muscle during exercise

The turnover of adenosine triphosphate (ATP) in vertebrate skeletal muscle can increase more than a hundredfold during high-intensity exercise while the content of ATP in muscle may remain virtually unchanged. This requires that the rates of ATP hydrolysis and ATP synthesis are exactly balanced despite large fluctuations in reaction rates. ATP is regenerated initially at the expense of phosphocreatine (PCr) and then mainly through glycolysis from muscle glycogen. The increased ATP turnover in contracting muscle will cause an increase in the contents of adenosine diphosphate (ADP), adenosine monophosphate (AMP) and inorganic phosphate (P_i), metabolites that are substrates and activators of regulatory enzymes such as glycogen phosphorylase and phosphofructokinase. An intracellular metabolic feedback mechanism is thus activated by muscle contraction. How muscle metabolism is integrated in the intact body under physiological conditions is not fully understood. Common frogs are suitable experimental animals for the study of this problem because they can readily be induced to change from rest to high-intensity exercise, in the form of swimming. The changes in metabolites and effectors in gastrocnemius muscle were followed during exercise, post-exercise recovery and repeated exercise. The results suggest that glycolytic flux in muscle is modulated by signals from outside the muscle and that fructose 2,6-bisphosphate is a key signal in this process.     

Glycogen and phosphorylase in Klinefelter's syndrome: a histochemical study

Summary The behaviour of glycogen and phosphorylase in Klinefelter's syndrome has been studied using histochemical techniques.     

Effect of X-irradiation on phosphorylase activity in tissues of pregnant mice

Résumé Les niveaux de phosphorylase du foie et du placenta maternels oscillent, mais chez les souris, ceux du foie foetal augmentent constamment pendant la grossesse. L'effet des rayons X sur la phosphorylase du foie foetal est relativement plus élevé.     

Flying insects: model systems in exercise physiology

Insect flight is the most energy-demanding exercise known. It requires very effective coupling of adenosine triphosphate (ATP) hydrolysis and regeneration in the working flight muscles.³¹P nuclear magnetic resonance (NMR) spectroscopy of locust flight muscle in vivo has shown that flight causes only a small decrease in the content of ATP, whereas the free concentrations of inorganic phosphate (P _i ), adenosine diphosphate (ADP) and adenosine monophosphate (AMP) were estimated to increase by about 3-, 5- and 27-fold, respectively. These metabolites are potent activators of glycogen phosphorylase and phosphofructokinase (PFK). Activation of glycolysis by AMP and P _i is reinforced synergistically by fructose 2,6-bisphosphate (F2,6P₂), a very potent activator of PFK. During prolonged flight locusts gradually change from using carbohydrate to lipids as their main fuel. This requires a decrease in glycolytic flux which is brought about, at least in part, by a marked decrease in the content of F2,6P₂ in flight muscle (by 80% within 15 min of flight). The synthesis of F2,6P₂ in flight muscle can be stimulated by the nervous system via the biogenic amine octopamine. Octopamine and F2,6P₂ seem to be part of a mechanism to control the rate of carbohydrate oxidation in flight muscle and thus function in the metabolic integration of insect flight.Dedicated to Dr. Ernst Zebe, Emeritus Professor of Zoology (University of Münster) on the occasion of his 70th birthday.     

Structure and function of small heat shock/alpha-crystallin proteins: established concepts and emerging ideas

Small heat shock/alpha-crystallin proteins are defined by conserved sequence of approximately 90 amino acid residues, termed the alpha-crystallin domain, which is bounded by variable amino- and carboxy-terminal extensions. These proteins form oligomers, most of uncertain quaternary structure, and oligomerization is prerequisite to their function as molecular chaperones. Sequence modelling and physical analyses show that the secondary structure of small heat shock/alpha-crystallin proteins is predominately beta-pleated sheet. Crystallography, site-directed spin-labelling and yeast two-hybrid selection demonstrate regions of secondary structure within the alpha-crystallin domain that interact during oligomer assembly, a process also dependent on the amino terminus. Oligomers are dynamic, exhibiting subunit exchange and organizational plasticity, perhaps leading to functional diversity. Exposure of hydrophobic residues by structural modification facilitates chaperoning where denaturing proteins in the molten globule state associate with oligomers. The flexible carboxy-terminal extension contributes to chaperone activity by enhancing the solubility of small heat shock/alpha-crystallin proteins. Site-directed mutagenesis has yielded proteins where the effect of the change on structure and function depends upon the residue modified, the organism under study and the analytical techniques used. Most revealing, substitution of a conserved arginine residue within the alpha-crystallin domain has a major impact on quaternary structure and chaperone action probably through realignment of beta-sheets. These mutations are linked to inherited diseases. Oligomer size is regulated by a stress-responsive cascade including MAPKAP kinase 2/3 and p38. Phosphorylation of small heat shock/alpha-crystallin proteins has important consequences within stressed cells, especially for microfilaments.     

Characterization and antithrombotic action of tissue plasminogen activator

An extractive fibrinolytic enzyme has been characterized and found to belong to the class of vascular plasminogen activators. The agent has been found to have an antithrombotic action in the rabbit.     

Binding site of activators of the cystic fibrosis transmembrane conductance regulator in the nucleotide binding domains

The use of substances that could activate the defective chloride channels of the mutant cystic fibrosis transmembrane conductance regulator (CFTR) has been suggested as possible therapy for cystic fibrosis. Using epithelia formed by cells stably transfected with wildtype or mutant (G551D, G1349D) CFTR, we estimated the apparent dissociation constant, K_D, of a series of CFTR activators by measuring the increase in the apical membrane current. Modification of apparent K_D of CFTR activators by mutations of the nucleotide-binding domains (NBDs) suggests that the binding site might be in these regions. The human NBD structure was predicted by homology with murine NBD1. An NBD1-NBD2 complex was constructed by overlying monomers to a bacterial ABC transporter NBD dimer in the head-to- tail conformation. Binding sites for CFTR activators were predicted by molecular docking. Comparison of theoretical binding free energy estimated in the model to free energy estimated from the apparent dissociation constants, K_D, resulted in a remarkably good correlation coefficient for one of the putative binding sites, located in the interface between NBD1 and NBD2.Received 21 September 2004; received after revision 6 December 2004; accepted 10 December 2004     

Étude de l'activité in vitro de la glycogène phosphorylase de la Carpe (Cyprinus carpio L.)

Summary In this paper we give some values of glycogen phosphorylase activity of heart, red muscle and white muscle from the Carp. We show that in vitro optimum temperature is 25°C for the fish, and not 30°C as in Mammalians. We also made measurements with rat and tench liver, but it has been impossible, under the same experimental conditions, to observe normal release of inorganic phosphorus from G-1-P with carp liver.     

Phosphorylase activity of human placenta perfused in vitro: effect of gonadotropins, dibutyryl cyclic AMP and prostaglandins]

The gonadotropic hormones stimulate the glycogen phosphorylase activity of human full-term placenta perfused in vitro. This effect is reproduced by dibutyryl cAMP and PG F2alpha and accompanied by an increased glucose liberation in the perfusion fluid.     

Contributions in the domain of cancer research: Review¶Negative regulators of cyclin-dependent kinases and their roles in cancers

In the past decade, the discovery and characterization of cyclin-dependent kinases (CDKs), the engine cores of the cell cycle machinery, have advanced our understanding of the cell cycle. Both positive and negative regulators of CDKs have been characterized, accelerating the important research to unravel the mechanisms of the cell cycle disease--cancer. Cancer can originate from overexpression of positive regulators, such as cyclins, or from underexpression of negative regulators, such as CDK inhibitors (CKIs). CKIs are the focus of much cancer research because they are capable of controlling cell cycle proliferation--the Holy Grail for cancer treatment. CDKs can be inactivated by several mechanisms:, (i) by association with CKIs including p16 (INK4a), p15 (INK4b), p21 (Cip1), p27 (Kip1), and p57 (Kip2), (ii) by disassociation from their cyclin regulatory unit, (iii) by dephosphorylation of a conserved threonine residue in the T-loop, and (iv) by adding inhibitory phosphate. Here we discuss what is known about each mechanism with a hope that these insights will become useful in developing strategies to eliminate cancer in the future.     

Stimulation of gastric secretion by prostaglandin F2 alpha in rats.

In rats with chronic gastric fistulas, prostaglandin F2 alpha stimulated the gastric acid secretion in graded doses of 50, 100, 200 and 400 microgram/kg b.wt, while higher doses above 1 mg/kg b.wt tended to inhibit significantly. The gastric antisecretory effect of prostaglandin E1 could not be altered or modified by subsequent treatment of prostaglandin F2 alpha, while the latter alone without any prior treatment of the former, stimulated output of gastric juice, HCl and pepsin without significantly affecting the concentration of these components.     

Human sulfatases: A structural perspective to catalysis

The sulfatase family of enzymes catalyzes hydrolysis of sulfate ester bonds of a wide variety of substrates. Seventeen genes have been identified in this class of sulfatases, many of which are associated with genetic disorders leading to reduction or loss of function of the corresponding enzymes. Amino acid sequence homology suggests that the enzymes have similar overall folds, mechanisms of action, and bivalent metal ion-binding sites. A catalytic cysteine residue, strictly conserved in prokaryotic and eukaryotic sulfatases, is post-translationally modified into a formylglycine. Hydroxylation of the formylglycine residue by a water molecule forming the activated hydroxylformylglycine (a formylglycine hydrate or a gem-diol) is a necessary step for the enzyme's sulfatase activity. Crystal structures of three human sulfatases, arylsulfatases A and B(ARSA and ARSB), and estrone/dehydroepiandrosterone sulfatase or steroid sulfatase (STS), also known as arylsulfatase C, have been determined. While ARSA and ARSB are water-soluble enzymes, STS has a hydrophobic domain and is an integral membrane protein of the endoplasmic reticulum. In this article, we compare and contrast sulfatase structures and revisit the proposed catalytic mechanism in light of available structural and functional data. Examination of the STS active site reveals substrate-specific interactions previously identified as the estrogen-recognition motif. Because of the proximity of the catalytic cleft of STS to the membrane surface, the lipid bilayer has a critical role in the constitution of the active site, unlike other sulfatases.     

Characterization and antithrombotic action of tissue plasminogen activator

Summary An extractive fibrinolytic enzyme has been characterized and found to belong to the class of vascular plasminogen activators. The agent has been found to have an antithrombotic action in the rabbit.Provided by Dr L. Dussourd d'Hinterland, Laboratoires Pierre Fabre, Castres, France. 1000 units have a fibrinolytic activity of about 15 PU urokinase.