Dephosphorylation, oxidative

Figure 2. Mechanism of PDH. The three different subunits of the PDH complex in the mitochondrial matrix (E, pyruvate decarboxylase E2, dihydrolipoamide acyltrans-ferase Ej, dihydrolipoamide dehydrogenase) catalyze the oxidative decarboxylation of pyruvate to acetyl-CoA and CO2. E, decarboxylates pyruvate and transfers the acetyl-group to lipoamide. Lipoamide is linked to the group of a lysine residue to E2 to form a flexible chain which rotates between the active sites of E, E2, and E3. E2 then transfers the acetyl-group from lipoamide to CoASH leaving the lipoamide in the reduced form. This in turn is oxidized by E3, which is an NAD-dependent (low potential) flavoprotein, completing the catalytic cycle. PDH activity is controlled in two ways by product inhibition by NADH and acetyl-CoA formed from pyruvate (or by P-oxidation), and by inactivation by phosphorylation of Ej by a specific ATP-de-pendent protein kinase associated with the complex, or activation by dephosphorylation by a specific phosphoprotein phosphatase. The phosphatase is activated by increases in the concentration of Ca in the matrix. The combination of insulin with its cell surface receptor activates PDH by activating the phosphatase by an unknown mechanism.

Serine. Oxidation of the a-hydroxyl group of the glycolytic intermediate 3-phosphoglycerate converts it to an 0x0 acid, whose subsequent transamination and dephosphorylation leads to serine (Figure 28—5). 

Insulin binding to the extracellular side of cell membranes initiates the insulin cascade , a series of phosphorylation/dephosphorylation steps. A postulated mechanism for vanadium is substitution of vanadate for phosphate in the transition state structure of protein tyrosine phosphatases (PTP).267,268 In normal physiological conditions, the attainable oxidation states of vanadium are V111, Viv and Vv. Relevant species in solution are vanadate, (a mixture of HV042-/ H2VOO and vanadyl V02+. Vanadyl is not a strong inhibitor of PTPs, suggesting other potential mechanisms for insulin mimesis for this cation. 

Under the conditions of low illumination (normally shady light, which has a high proportion of long-wavelength red light), PS I takes electrons faster than PS II can supply, leaving plastoquinone in its oxidized state. As a result, LHCs are dephosphorylated and migrate to the stacked portion of the thylakoid membrane where they drive to PS II. 

Fig. 13.6 A m ulti-enzyme one-pot example cascade conversion of glycerol into a heptose sugar through consecutive phosphorylation, oxidation, aldol reaction and dephosphorylation [11],...

Fig. 9.12. Mechanism of monooxygenase-catalyzed oxidative desulfuration and dephosphorylation of phosphorothioates (9.67, X = O) and phosphorodithioates (9.67, X = S). The first step is believed to be an 5-oxygenation followed by rearrangement with sulfur expulsion (oxidative desulfuration) or hydrolysis to form phosphate and phosphorothioic 0,0-acid diesters.

Psilocybin (Figure 3.5a) and psilocin (Figure 3.5b) are indole derivatives substituted in position 4 by a hydroxyl group, where psilocybin is phosphory-lated. Due to its ionic properties, psilocybin is soluble in water. In addition, phosphorylation protects psilocybin from oxidative degradation. Both compounds are found to affect laboratory animals, but there is evidence that only the dephosphorylated form, psilocin, is the active species. In their structure the toxins resemble serotonine, a biogenic amine known to be a neurotransmitter. 

GTPCH (EC 3.5.4.16) converts the substrate GTP to 7,8-dihydroneopterin triphosphate (H2NTP) and formate. GTPCH activity is determined by measuring neopterin, the completely oxidized and dephosphorylated H TP-product of the enzyme reaction. Conversion of H2NTP to neopterin is carried out after the enzymatic reaction in presence of iodine at pH 1.0, followed by dephosphorylation with alkaline phosphatase at pH 8.5-9.0. Neopterin is detected fluorimetrically at 350/440 nm upon HPLC separation. The assay is based with some modifications on the methods published by Viveros et al. and Hatakeyama and Yoneyama [15,16]. 

Besides the enzymatic incubation in the reaction mixture, all procedures are carried out at 4°C. GTPCH activity is assayed by measuring the neopterin produced upon enzymatic incubation at 37°C for 60 min in a final volume of 0.1 ml in the dark (due to light sensitivity of pterins), followed by chemical oxidation and dephosphorylation. Two separate blanks are prepared, a blank reaction with cell lysate that is immediately oxidized to detect the neopterin that was present in the lysate, and a blank reaction without cell lysate to detect the neopterin that is generated from the incubation (substrate) buffer. The sum of both blanks is later subtracted from the value of the incubation reaction to determine the enzymatically produced neopterin. 

S ATP -P acetate <1-18> (<8> acetate kinase/phosphotransacetylase, major role of this two-enzyme sequence is to provide acetyl coenzyme A which may participate in fatty acid synthesis, citrate formation and subsequent oxidation [1] <3> function in the metabolism of pyruvate or synthesis of acetyl-CoA coupling with phosphoacetyltransacetylase [15] <11> function in the initial activation of acetate for conversion to methane and CO2 [19] <10> key enzyme and responsible for dephosphorylation of acetyl phosphate with the concomitant production of acetate and ATP [30]) (Reversibility r <1-18> [1, 2, 5-21, 24-27, 29-33]) [1, 2, 5-21, 24-27, 29-33]... 

TorR -I- ATP <103> (<103>, TorS is a sensor that contains three phosphorylation sites and transphosphorylates TorR via a four-step phosphorelay, His443 to Asp723 to His850 to Asp(TorR). TorS can dephosphorylate phospho-TorR when trimethylamine N-oxide is removed. Dephosphorylation probably occurs by a reverse phosphorelay, Asp(TorR) to His850 to Asp723 [167]) (Reversibility <103> [167]) [167]... 

Glucose 6-phosphate is the key intermediate in carbohydrate metabolism. It may be polymerized into glycogen, dephosphorylated to blood glucose, or converted to fatty acids via acetyl-CoA. It may undergo oxidation by glycolysis, the citric acid cycle, and respiratory chain to yield ATP, or enter the pentose phosphate pathway to yield pentoses and NADPH. 

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