5-Nucleotidase

REIs [1934] described' an enzyme, called by him 5-nucleotidase, which occurs in the brain of the rabbit and rat and in the retina of the frog, rat, rabbit and calf.Extracts of these tissues dephosphorylated muscle adenylic acid (adenosine-5phosphate) and inosinic acid (inosine-5-phosphate) many times more rapidly than yeast adenylic acid (adenosine-3-phosphate) or glycerophosphate.Subsequently, Reis [1937] showed the presence of the same enzyme in calf brain and horse nerve, and extended the list of substances which are only slowly dephosphorylated to include Embden's hexosemonophosphate, pyrophosphate, phosphoglyceric acid, phosphogluconic acid and guanine nucleotide.He attri- buted this unspecific hydrolysis to the action of a general phosphatase present in small amount in nervous tissue, whereas the rapid fission of adenosine (inosine)-5-phosphate is caused by 5-nucleotidase.The position of Harden & Young's fructose-1:6-diphosphate was inter- mediate between that of adenosine-5-phosphate and that of the group of slightly reactive substances.Reis attributed this to the presence of the furanose ring in fructose-1:6-diphosphate, a structure also found in adenosine-5-phosphate but not in Embden's hexosemonophosphate, which is a pyranose.In connexion with the present investigations, it should be noted that the duration of the experiments of Reis did not exceed 5 hr.