Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Although there is some evidence that extrachoroidal sites for the production of cerebrospinal fluid (CSF) are important, the choroid plexuses in the ventricles contribute the major part of CSF formation. The exact mechanism for CSF production is not fully understood. In order to study this mechanism from the enzyme histochemical standpoint, the previously reported studies are reviewed, in addition to the authors' own electron microscopic enzyme histochemical observations on this tissue. The ultrastructure and enzyme biochemistry of choroid plexus epithelial cells are considered, together with the histochemistry of the following enzymes: alkaline and acid phosphatase, Mg2+-ATPase, Na+, K+-ATPase, glucose-6-phosphatase, thiamine pyrophosphatase, adenylate cyclase, carbonic anhydrase, oxidoreductase, esterase, several hydrolases, and other enzymes. Finally, CSF formation and active transport in the choroid plexus epithelial cells are discussed, mainly in terms of the results of our enzyme cytochemical observations on Na+, K+-ATPase and carbonic anhydrase in this tissue.
 ...
PMID:The enzyme histochemistry of the choroid plexus. 683 Nov 99

The probable involvement of hepatic carbamyl-P in the reciprocal relationship between hepatic ureagenesis and glycogenesis from glucose was explored. Isolated perfused liver preparations from 48-h fasted rats were employed. Moderate (9.2 mM) and relatively high levels of glucose (34 mM) were perfused. Hepatic glycogenesis, glucose-6-P, carbamyl-P, and citrulline levels, hepatic urea formation, and ureagenesis based upon perfusate urea levels were measured. Experimental probes selected to modify hepatic ureagenesis and carbamyl-P production and utilization included: (a) NH4Cl, maintained at 5 mM by continuous infusion (NH4+ is a substrate for carbamyl-P synthase I and glutamate dehydrogenase); (b) norvaline, an inhibitor of ornithine transcarbamylase which catalyzes the first committed step in the urea cycle; and (c) ethoxyzolamide, an inhibitor of carbonic anhydrase which produces HCO3-, an essential substrate for carbamyl-P synthase I. NH4+ increased ureagenesis and decreased glycogenesis. The inclusion of norvaline with NH4+ decreased ureagenesis and increased glycogenesis. Ethoxyzolamide with or without NH4+ inhibited both ureagenesis and glycogenesis, and decreased the hepatic glucose-6-P level. Glycogenesis was greater at 34 mM than 9.2 mM glucose, increased in norvaline-containing preparations correlative with increased availability of carbamyl-P, and decreased when carbamyl-P formation was inhibited by ethoxyzolamide. Kinetic analysis indicated a Km, Glc of 31 mM for glucose phosphorylation preliminary to glycogenesis. Glycogen formation via the "indirect pathway" (i.e. involving extrahepatic glycolysis, transport of lactate to the liver, and glyconeogenesis therefrom) was quantitatively insufficient to account for the observed glycogenesis. Glucokinase is contraindicated by the inverse relationship between hepatic glycogenesis and ATP availability in the ethoxyzolamide-treated preparations. In contrast, carbamyl-P:glucose phosphotransferase activity of the glucose-6-phosphatase system has the characteristics to bridge hepatic ureagenesis and glycogenesis.
 ...
PMID:Glycogenesis from glucose and ureagenesis in isolated perfused rat livers. Influence of ammonium ion, norvaline, and ethoxyzolamide. 813 5

Little is known about the development of the central nervous system (CNS) in humans. Ethical considerations preclude experimental studies in this field, and as a result most available data on human ontogenesis are descriptive. Comparative anatomic and embryologic studies have demonstrated that the main developmental milestones are conserved across species, and their results can be used to suggest a likely scenario for human development. The development of the ventricles, meninges, and choroid plexuses are discussed in this article. The central cavity of the neural tube is formed during neurulation, which occurs during the fourth gestational week. The first milestone is occlusion of the spinal neurocele (the central canal in the neural tube) shortly after neurulation. This prevents free communication between the ventricular system and the amniotic cavity. The second milestone is development of the meninges, which separate the central nervous system from the rest of the body. The embryonic origin of the meninges varies across species. In birds (and probably in mammals), the spinal meninges are derived from the somitic mesoderm, the brainstem meninges from the cephalic mesoderm, and the telencephalic meninges from the neural crest. Differentiation of the meninges, which involves formation of the subarachnoid space, occurs early, before the cerebrospinal fluid (CSF) begins to flow around the CNS. During ontogenesis, the meninges play a key role in regulating the growth of underlying nervous structures. They induce the formation of the superficial glial limiting layer and stimulate the growth of precursors located in the superficial blastemas of the cerebellum and hippocampus. The choroid plexuses are complex specialized structures that produce most of the CSF. Their epithelium derives from the neural tube epithelium and their mesenchyma from the meninges. Of the many enzymes produced in the choroid plexuses, some reflect the pivotal metabolic role of these structures (alkaline and acid phosphatases, magnesium-dependent ATPase, glucose-6-phosphatase, thiamine pyrophosphatase, adenylate cyclase, oxidoreductase, esterases, hydrolases, cathepsin D, and glutathion S-transferase). The two enzymes that are crucial to the production of CSF are Na+/K+ ATPase and carbonic anhydrase. Inactivation of catecholamines is mediated by catechol-O-methyltransferase and by the monoamine oxidases A and B. The morphology and synthesis profile of the choroid plexuses changes during development, although little is known about these changes in humans.
 ...
PMID:Embryonic and fetal development of structures associated with the cerebro-spinal fluid in man and other species. Part I: The ventricular system, meninges and choroid plexuses. 975 71