Adenosine diphosphate dephosphorylation

Approximately 80% of red blood cell purines are in the form of adenosine triphosphate (ATP) with an intracellular concentration estimated to be 2-3 mM. In glucose-deprived or aged red cells there is a progressive decline in the ATP content of the erythrocyte leading to the formation of adenosine diphosphate (ADP) and adenosine monophosphate (AMP) AMP is then dephosphorylated (via 5 -nucleotidase) to... 

The conversion of pyruvate to fatty acids requires a source of acetyl CoA in the cytosol. Pyruvate can only be converted to acetyl CoA in mitochondria, so it enters mitochondria and forms acetyl CoA through the pyruvate dehydrogenase (PDH) reaction. This enzyme is dephosphorylated and most active when its supply of substrates and adenosine diphosphate (ADP) is high, its products are used, and insulin is present (Fig. 36.3). 

The biologically active R- or 5 -pantothenic acid can be obtained upon hydrolysis of coenzyme A with a combiaation of two enzymes, alkaline phosphatase and pantotheiaase (13) (Fig. 1). The phosphatase catalyzes the selective cleavage of the phosphate bond ia coenzyme A to afford adenosin-3 5 -diphosphate (6) and 4-phosphopantetheiae (7). The latter substance is dephosphorylated enzymatically to yield pantetheiae (8), which is rapidly converted by pantotheiaase to pantothenic acid (1). Table 1 Hsts some physical properties of pantothenic acid and its derivatives. 

The enzyme purified from bull semen dephosphorylates the 5 -phosphate esters of adenosine, uridine, cytidine, guanosine, nicotinamide riboside, and the 5 -phosphate esters of deoxynucleosides, but is inactive with adenosine pyrophosphates and substrates which bear other substituents on the ribose, e.g., adenosine 2, 5 -diphosphate (124). However 5 -nucleo-tidase from potato can hydrolyze the 5 -phosphate of this diphosphate... 

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