Phosphorylation, adenosine hexokinase

Another enzyme used for the measurement of glucose is hexokinase (EC 2.7.1.1) which catalyses the phosphorylation of glucose to produce glucose-6-phosphate with adenosine triphosphate as the phosphate donor and magnesium ions as an activator. The rate of formation of glucose-6-phosphate can be linked to the reduction of NADP by the enzyme glucose-6-phosphate dehydrogenase (EC 1.1.1.49). This indicator reaction can be monitored spectrophotometrically at 340 nm or fluorimetrically ... 

Glucose and fructose are phosphorylated in the presence of adenosine triphosphate (ATP) in a reaction is catalysed by hexokinase (HK) producing respectively, glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P) ... 

The rate of D-glucosamine phosphorylation is about 70% of that for D-glucose phosphorylation. Free D-glucosamine and adenosine-5-tri-phosphoric acid disappear at similar rates in the presence of yeast hexokinase. ... 

In the liver, kidney, and intestine, fructose can be converted to glycolytic/ gluconeogenic intermediates by the actions of three enzymes—fructokinase, aldolase B, and triokinase (also called triose kinase)—as shovra in Figure 24-1. In these tissues, fructose is rapidly phosphorylated to fructose 1-phosphate (FIP) by fructokinase at the expense of a molecule of adenosine triphosphate (ATP). This has the effect of trapping fructose inside the cell. A deficiency in this enzyme leads to the rare but benign condition known as essential fmcto-suria. In other tissues such as muscle, adipose, and red blood cells, hexokinase can phosphorylate fructose to the glycolytic intermediate fmctose 6-phosphate (F6P). 

This simple metabolic process occurs anaerobically by a series of enzymes involved in a pathway called glycolysis (Fig. 3-4), in which glucose, a 6-carbon sugar, is converted ultimately to p)rruvic acid. Initially, the glucose is phosphorylated by the enzyme hexokinase which requires ATP (adenosine triphos-... 

This is the first reaction in the biochemical pathway called glycolysis. A phosphoryl group is transferred from a donor molecule, adenosine triphosphate, to the recipient molecule, glucose. The products are glucose-6-phosphate and adenosine diphosphate. This enz)rme, called hexokinase, is an example of a transferase. 

Kinases are enzymes that transfer a phosphate group from adenosine triphosphate (ATP), or other trinucleotide, to a number of biological substrates, such as sugars or proteins. They are part of a larger family of enzymes known as group transferases, but are limited to phosphate transfers. A typical reaction catalyzed by a kinase (e.g., hexokinase) is the phosphorylation of glucose upon its entry into a cell... 

Adenosine triphosphate, ATP, phosphorylates glncose as it enters the living cell according to reaction (11.36), which can alternatively be written as (11.37). In this non-reversible reaction in which ATP acts as the phosphorylating agent, the enzyme is given a special name hexokinase (Fignre 11.14). Enzymes which catalyse transfers specifically to and from ATP (or other nucleotides) are sometimes called phosphokinases. 

The enzyme hexokinase, in common with other kinases that catalyse phosphorylation reactions, requires adenosine triphosphate (ATP) as the substrate. The latter is converted to adenosine diphosphate (ADP) during the reaction and must be recycled to avoid the consumption of stoichiometric amounts of the ATP. This can be readily achieved by the introduction of a second enzyme reaction which converts ADP back to ATP. Thus, pyruvate kinase phosphorylates ADP using phosphoenol pyruvate as the phosphate donor, yielding ATP and pyruvic acid. In this way, these phosphorylation reactions can be carried out using a catalytic amount of ATP provided that a stoichiometric quantity of phosphoenol pyruvate is used (Scheme 5.27). 

Hexokinase (EC 2.7.1.1), for example, catalyses the phosphorylation of a number of hexoses with adenosine triphosphate. 

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