Phosphorylation ATP-dependent

T"he extraordinary ability of an enzyme to catalyze only one particular reaction is a quality known as specificity (Chapter 14). Specificity means an enzyme acts only on a specific substance, its substrate, invariably transforming it into a specific product. That is, an enzyme binds only certain compounds, and then, only a specific reaction ensues. Some enzymes show absolute specificity, catalyzing the transformation of only one specific substrate to yield a unique product. Other enzymes carry out a particular reaction but act on a class of compounds. For example, hexokinase (ATP hexose-6-phosphotransferase) will carry out the ATP-dependent phosphorylation of a number of hexoses at the 6-posi-tion, including glucose. 

Riboflavin fulfills its role in metabolism as the coenzymes flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) (Figure 45-10). FMN is formed by ATP-dependent phosphorylation of riboflavin, whereas FAD is synthesized by further reaction of FMN with ATP in which its AMP moiety is transferred to the... 

A common intermediate for all the nucleotides is 5-phosphoribosyl-l-diphosphate (PRPP), produced by successive ATP-dependent phosphorylations of ribose. This has an a-diphosphate leaving group that can be displaced in Sn2 reactions. Similar Sn2 reactions have been seen in glycoside synthesis (see Section 12.4) and biosynthesis (see Box 12.4), and for the synthesis of aminosugars (see Section 12.9). For pyrimidine nucleotide biosynthesis, the nucleophile is the 1-nitrogen of uracil-6-carboxylic acid, usually called orotic acid. The product is the nucleotide orotidylic acid, which is subsequently decarboxylated to the now recognizable uridylic acid (UMP). 

Interconversion processes in most cases involve ATP-dependent phosphorylation of... 

This enzyme [EC 2.7.1.60] catalyzes the ATP-dependent phosphorylation of A-acylmannosamine to yield ADP and A-acylmannosamine 6-phosphate. The enzyme can act on both the acetyl and the glycolyl derivatives. 

Any of a broad class of phosphoryl-transfer enzymes [EC 2.7.1.x] that catalyze the ATP-dependent phosphorylation of proteins, most often occurring at seryl, threo-nyl, and tyrosyl residues. These enzymes are central participants in cellular signal transduction pathways, and their discovery and recognition as primary control components of the cell culminated in the award of the 1992 Nobel Prize in Medicine and Physiology to American enzymologists Edwin Krebs and Edward Fischer. There is reason to believe that approximately 2% of the coding sequences in the human genome specify some 2000 different kinases that phosphorylate protein substrates. The prototypical enzyme is known as 3, 5 -cAMP-stimulated protein kinase (or, protein kinase A). See specific protein kinase... 

Calculate Keq for the overall reaction. For the ATP-dependent phosphorylation of glucose, what concentration of glucose is needed to achieve a 250 /xm intracellular concentration of glucose 6-phosphate when the concentrations of ATP and ADP are 3.38 mM and 1.32 mM, respectively Does this coupling process provide a feasible route, at least in principle, for the phosphorylation of glucose in the cell Explain. 

CPSase catalyzes the formation of carbamyl phosphate from glutamine, bicarbonate, and two equivalents of ATP. The biosynthesis involves four partial reactions. GLNase catalyzes the formation of ammonia from glutamine. The remaining three partial reactions are catalyzed by SYNase. Bicarbonate is activated by ATP to form carboxyphosphate, which reacts with ammonia to form carbamate. The ATP-dependent phosphorylation of carbamate results in the production of carbamyl phosphate. 

Regulation of glycogen phosphorylase in muscle is accomplished by many of the same enzymes that control glycogen synthesis. Phosphorylase kinase converts the dimeric phosphorylase from the inactive to the active form by Mg + and ATP-dependent phosphorylation of two identical serine residues. The principal enzyme that removes this phosphate may be protein phosphatase-1 (phosphorylase phosphatase). 

PanK (EC 2.7.1.33) catalyzes the first and committed step of CoA biosynthesis the ATP-dependent phosphorylation of pantothenic acid 2 to form 4 -phosphopantothenate 8 (Equation (1)). 

Hexokinase catalyzes the ATP-dependent phosphorylation of a broad spectrum of 6-carbon sugars. In the reaction involving glucose and ATP, glucose-6-phosphate (G6P) and ADP are formed. 

Gly3P is formed from glycerol by ATP-dependent phosphorylation catalyzed by glycerol kinase. 

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