Removal of phosphate groups

Many enzymes may be regulated by covalent modification, most frequently by the addition or removal of phosphate groups from specific serine, threonine, or tyrosine residues of the enzyme. Protein phosphorylation is recognized as one of the primary ways in which cellular processes are regulated. 

Covalent modification by the addition and removal of phosphate groups. 

Many enzymes are regulated by covalent modification, most frequently by the addition or removal of phosphate groups from specific serine, threonine, or tyrosine residues of the enzyme. In the fed state, most of the enzymes regulated by covalent modification are in Ihe dephosphorylated form and are active (see Figure 24.2). Three exceptions are glycogen phosphorylase (see p. 129), fructose bis-phosphate phosphatase-2 (see p. 98), and hormone-sensitive lipase of adipose tissue (see p. 187), which are inactive in their dephosphorylated state. 

Another important hydrolytic enzyme of the gut is acid phosphatase Like enterokinasc, it is bound to the enierocyte facing the lumen and is present in the duodenum, jejunum, and ileum. Alkaline phosphatase, a zinc metalloenzyme, also occurs in the gut. Acid phosphatase and alkaline phosphatase catalyze the removal of phosphate groups from a wide variety of compounds in foods, for example, sugar phosphates, triose phosphates, nucleotides such as AMP, ADP, and ATP, pyrophosphate, and phosphorylaled amino adds, A number of sugar and triose phosphates are described in the section on glycolysis in Chapter 4,... 

Phosphorylation is carried by enzyme protein kinases. The phosphorylated proteins may undergo the process of dephosphorylation by removal of phosphate group(s). The dephosphorylation is catalyzed by another enzyme... 

Phosphoprotein phosphatases are responsible for the cleavage of phosphate groups from their protein acceptors. Some reports suggest that these enzymes can be inhibited by zinc. The actions of cAMP, then, can be seen to be terminated by two mechanisms the breakdown of cAMP by phosphodiesterase and the removal of phosphate groups from phosphoproteins by phosphatases. 

ADP adenosine diphosphate produced by removal of phosphate group from ATP Adrenoreceptors - receptors for noradrenaline in the sympathetic nervous system Adverse reaction - any reaction to a drug that is harmful for the patient Agonist - drug that activates receptors to produce a response... 

GTP - guanine triphosphate - transfers phosphate groups in cellular reactions GTPase - enzyme that converts GTP into GDP by removal of phosphate group HDL high-density lipoprotein - small lipoprotein circulating in blood mops up cholesterol... 

Phosphorylation of serine residue(s) of the j8-subunit of the carboxyltransferase unit occurs in pea chloroplasts incubated in the light [20]. Alkaline phosphatase treatment reduces ACC activity in parallel to removal of phosphate groups from ACC. This activation by phosphorylation is opposite to the inhibition of animal ACC by phosphorylation but is consistent with the increase in ATP concentration and rates of fatty acid synthesis in chloroplasts in the light and the activation of other plastid enzymes by phosphorylation. These results suggest that the CT subunit reaction is rate determining for overall ACC activity, at least for the multisubunits enzyme of dicots. 

Xu and co-workers reported the use of enz5miatic dephosphorylation to induce a sol-gel transition [86]. The small-molecule fluorenylmethyloxycarbonyl (FM0C]-t3n osine phosphate was exposed to a phosphatase, and the resulting removal of phosphate groups led to a reduction in electrostatic repulsions, supramolecular assembly by stacking of the fluorenyl groups, and eventual gelation. 

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