Adenosine triphosphate -Alcohol

Substitution of foreign metals for the metals in metalloenzymes (those that contain metals as part of their structures) is an important mode of toxic action by metals. A common mechanism for cadmium toxicity is the substitution of this metal for zinc, a metal that is present in many metalloenzymes. This substitution occurs readily because of the chemical similarities between the two metals (for example, Cd2+ and Zn2+ behave alike in solution). Despite their chemical similarities, however, cadmium does not fulfill the biochemical function of zinc and a toxic effect results. Some enzymes that are affected adversely by the substitution of cadmium for zinc are adenosine triphosphate, alcohol dehydrogenase, and carbonic anhydrase. 

Vinyl alcohol copolymer gel is hydrophilic and has been developed for aqueous-phase size-exclusion liquid chromatography however, it is less polar than the polysaccharides. Its specificity permits the direct injection of a biological sample without deproteinization. For example, blood serum from a patient suffering from chronic nephritis has been injected directly as a measure of the degree of dialysis (Figure 3.17). Adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate in red blood cells have also been separated directly (Figure 3.18). Theophylline in blood serum has been... 

Figure 3.18 Adenosine phosphates in blood on vinyl polymer column. Conditions column, Asahipak GS320 (vinyl alcohol copolymer gel), 50 cm x 7.6 mm i.d. eluent, 0.1 M sodium phosphate buffer containing 3 M sodium chloride pH 7.0 flow rate, 1.0 ml min-, detection, UV 260 nm. Peaks 1, haemoglobin 2, adenosine triphosphate 3, adenosine diphosphate and 4, adenosine monophosphate.

An alcohol can react with phosphoric acid to produce a phosphate ester iphosphoester). When two phosphate groups are joined, the resulting bond is a phosphoric anhydride bond. These two functional groups are important to the structure and fimction o( adenosine triphosphate (ATP), the universal energy currency of all cells. Cellular enzymes can carry out a reaction between a thiol and a carboxylic acid to produce a thioester. This reaction is essential for the activation of acyl groups in carbohydrate and fatty acid metabolism. Coenz)une A is the most important thiol involved in these pathways. 

Ethanol is a dietary fuel that is metabolized to acetate principally in the liver, with the generation ofNADH. The principal route for metabolism of ethanol is through hepatic alcohol dehydrogenases, which oxidize ethanol to acetaldehyde in the cytosol (Fig. 25.1). Acetaldehyde is further oxidized by acetaldehyde dehydrogenases to acetate, principally in mitochondria. Acetaldehyde, which is toxic, also may enter the blood. NADH produced by these reactions is used for adenosine triphosphate (ATP) generation through oxidative phosphorylation. Most of the acetate enters the blood and is taken up by skeletal muscles and other tissues, where it is activated to acetyl CoA and is oxidized in the TCA cycle. 

When mevalonate, written below as the anion of (iJ)-mevalonic add (Chapter 6, Section C, I and Chapter 11), is acted upon by the enzyme mevalonate-5-phosphotransferase, a phosphate unit is transferred from adenosine triphosphate (ATP) to the primary alcohol of mevalonate. Adenosine diphosphate (ADP) and phosphomevalonate are produced. Although enzyme mediated, this process may be viewed as the reaction of an activated derivative of phosphoric acid (an anhydride ) reacting with an alcohol to produce an ester of phosphoric acid [H3PO4 or 0=P(0H)3]. 

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