Diesterase, intestinal

If a-casein is treated with either the crystalline pyrophosphatase of yeast at pH 7.0 (35) or with the snake venom diesterase at pH 8.2 (87), no inorganic phosphorus is released. However, if the diesterase reaction is carried out in weakly buffered solutions a small drop of pH takes place (71), indicating the exposure of acidic groups. Subsequent incubation of the diesterase-treated a-casein with prostate phosphatase at pH 6.0 hberates no more phosphorus than in the absence of the diesterase. If, how ever, prostate and intestinal phosphatase are added, 78 % of the a-casein phosphorus is set free. Since the intestinal enzyme at pH 6.0 acts on low... 

Finally, if a-casein pretreated wdth the diesterase at pH 8.0 and the pyrophosphatase at pH 7.0 is exposed to the action of both the prostate and the intestinal enzyme, all of the phosphorus is liberated. These experiments thus demonstrate that a-casein contains 40% of its phosphorus as mono-0 O... 

Venom Phosphodiesterase. A phosphodiesterase from the venom of several species of snakes exhibits extreme specificity with regard to nucleotides. It hydrolyzes only components from a phosphate esterified at a 5 position. Thus, 5 nucleotides are liberated from RNA. The venom diesterase attacks both purine and pyrimidine nucleotides (Fig. 26). This activity was useful in establishing that 3 -5 linkages, rather than 2 -3 linkages, occur in nucleic acids. A similar enzyme occurs in intestines. 

The 5 -Substituted Nucleotides. These are adenosine-5 -phosphate, guanosine-5 -phosphate, uridine-5 -phosphate, and cytidine-5 -phosphate. All of them have been found among the hydrolysis products when ribonucleic acid is treated with snake venom diesterase or with intestinal phosphatase in the presence of arsenate. These compounds contain phosphate esterified at carbon 5 of the ribose moiety. 

Snake venom diesterase and intestinal mucosa diesterase are thought to cleave the phospho-diester bond, as indicated by the dotted lines in (VIII). It can be seen that splitting in this manner would yield a mixture of nucleoside-5 -phosphates. 

Desoxyribonucleic acid is hydrolyzed by calf intestinal diesterase to give a mixture of mononucleotides.Phosphatase activity present in the enzyme preparation must be inhibited by arsenate otherwise, nucleosides are obtained. The same nucleotide mixture results from the action of snake venom diesterase freed of phosphatase activity by chromatography on a cellulose column." ... 

Intestinal mucosa enzyme partially inhibited by arsenate leads to the formation of guanosine, cytidine, and cytidine-5 -phosphate. This preparation splits at (2) with subsequent partial dephosphorylation. Snake venom diesterase also sphts at (2). Prostatic phosphatase liberates... 

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