5-Nucleotidase

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Abstract
Extracts of calf and sheep retinae contain specific 5-nucleotidase. and during the early part of expts. rapidly dephosphorylate adenosine-5-phosphate but have only slight action on adenosine-3-phosphate. After an initial period in which the above conditions hold, dephosphoryla-tion of adenosine-3-phosphate occurs rapidly, and soon the degrees of hydrolysis of the 3- and 5-nucleotides become similar. Dialysis so alters retina extract that the specificity for adenosine-5-phosphate is lost and both 3- and 5-nucleotides are rapidly dephosphorylated immediately and at similar rates. It is concluded that retina extract contains considerable amounts of a phosphomonoesterase which, under suitable conditions, can dephosphorylate adenosine-3-phosphate. This view is contrary to the conclusion of Reis. The venoms of Russell''s viper, the water moccasin, the banded krait and the diamond rattlesnake, are rich and specific sources of 5-nucleotidase, since they rapidly dephosphorylate adenosine-5-phosphate and inosine-5-phosphate but have no action whatsoever on mono-phenyl-phosphate, [alpha] or [beta]-glycero-phosphate and adenosine-3-phosphate. Russell''s viper venom also failed completely to dephosphorylate 7 other monophosphoric esters. Taking into consideration the expts. of Reis, 5-nucleotidase dephosphorylates specifically adenosine-5-phosphate and ino-sine-5-phosphate but does not attack 15 other monophosphoric esters.

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