Glucose-6-phosphatase hormonal

Phosphoenolpyruvate carboxykinase (PEPCK) deficiency is distinctly rare and even more devastating clinically than deficiencies of glucose-6-phosphatase or fructose-1,6-bisphosphatase. PEPCK activity is almost equally distributed between a cytosolic form and a mitochondrial form. These two forms have similar molecular weights but differ by their kinetic and immunochemical properties. The cytosolic activity is responsive to fasting and various hormonal stimuli. Hypoglycemia is severe and intractable in the absence of PEPCK [12]. A young child with cytosolic PEPCK deficiency had severe cerebral atrophy, optic atrophy and fatty infiltration of liver and kidney. 

Responses of Activities of Glucose-6-phosphatase to Hormonal, Dietary, and Other Factors, in Vivo... 

His primary care physician obtained the following serum tests, which indicated liver damage alanine aminotransferase 103 U/L (reference 10-55 U/L) aspartate aminotransferase 967 U/L (reference 10-55 U/L) alkaline phosphatase level 125 U/L (reference 45-115 U/L) and total bilirubin 0.8mg/dL (reference 0-1.0 mg/dL). In addition, the serum glucose level was 711 mg/dL (reference 30-100 mg/dL). Decreased levels of follicle-stimulating and luteinizing hormones were also noted. 

In resting muscle, nearly all the enzyme is in the inactive b form. When exercise commences, the elevated level of AMP leads to the activation of phosphorylase b. Exercise will also result in hormone release that generates the phosphorylated a form of the enzyme. The absence of glucose 6-phosphatase in muscle ensures that glucose 6-phosphate derived from glycogen remains within the cell for energy transformation. 

Proximal tubule cells in culture should have retained functional attributes such as (1) polar architecture and junctional assembly of epithelia and correct membrane distribution of enzymes and transport systems (2) vectorial transport of solutes and water, manifested by the formation of domes when cultured on solid supports [81] and the generation of transepithelial electrophysiological properties [82, 83] due to the expression of proximal tubule specific claudins 2- and 10 [84, 85] (3) cellular uptake of xenobiotics from either the apical or basolateral side, as observed in vivo and (4) expression of nephron segment-specific characteristics, i.e., distinct expression of differentiation markers, metabolic and transport properties, and hormone responsiveness. Such markers include the expression of the brush border enzymes alkaline phosphatase, leucine aminopeptidase, and y-glutamyl transferase [4, 86], In addition, proximal tubule cells should possess Na+,K+-ATPase activities, Na+-dependent glucose, and p-aminohippurate transport. Proximal tubule cells increase cAMP levels in response to parathyroid... 

In some tissues, the phosphatase is regulated by hormones. In liver, epinephrine binds to the a-adrenergic receptor to initiate the phosphatidyl inositol pathway (p. 388), causing an increase in Ca" concentration that activates the phosphatase. In tissues capable of fatty acid synthesis, such as the liver and adipose tissue, insulin, the hormone that signifies the fed state, stimulates the phosphatase, increasing the conversion of pyruvate into acetyl Co A. Acetyl CoA is the precursor for fatty acid synthesis (p. 635). In these tissues, the pyruvate dehydrogenase complex is activated to funnel glucose to pyruvate and then to acetyl CoA and ultimately to fatty acids. 

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