Phosphodiesterase venom

FIGURE 11.31 Snake venom phosphodiesterase and spleen phosphodiesterase are exonncleases that degrade polynncleotides from opposite ends. 

Snake venom phosphodiesterase Both a Starts at 3 -end, 5 -NMP products... 

As for the stingray venom, not much is known. There was a report on the presence of 5 -nucleotidase and phosphodiesterase in stingray, Urolophus halleri, venom (29). 

Ribonucleoside 5 -0-hydroxymethylphosphonates (8 R = OH) are resistant to the action of phosphatases and phosphodiesterases. They are, however, good substrates for snake venom 5 -nucleotidase, unlike (8 R = H).2 ... 

Phosphoramidate analogues of dideoxyribonucleoside phosphates (26) and trideoxyribonucleoside phosphates are acid labile and can be hydrolysed enzymically. Snake venom phosphodiesterase cleaves (26) to thymidine and 5 -deoxy-5 -aminothymidine (27 R = H). The latter presumably arises by spontaneous decomposition of the phosphoramidate (27 R = PO3H2) and P—O fission must have occurred during the initial hydrolysis. With acid or spleen phosphodiesterase, (26) gave Tp and (27 R = H), i.e. P—N fission occurred. 

Using phosphotriester methods, dinucleoside (3 - 50-monophosphates containing 6-methyl-2,-deoxyuridine at the 3 - or 5 -end have been prepared.44 N.m.r. spectroscopy indicates that this nucleoside possesses the syn conformation in these compounds, and, on treatment with snake venom phosphodiesterase, d(m6UpT) is degraded, while d(Apm6U) is not, indicating that this enzyme, a 3 -exonuclease, requires the anti conformation to be present in the substrate. Two modified nucleo-side-5 -monophosphates, (20) and (21), which are resistant to 5 -nucleotidase, have been isolated from tRNA snake venom hydrolysates.45 A synthesis of (20) has been reported.46... 

Venom exonuclease [EC 3.1.15.1], also known as venom phosphodiesterase, catalyzes the exonucleolytic cleavage of RNA or DNA (preferring single-stranded substrates) in the 3 to 5 direction to yield 5 -phosphomononucleo-tides. Similar enzymes include hog kidney phosphodiesterase and the Lactobacillus exonuclease. See also specific phosphodiesterase J. A. Gerit (1992) The Enzymes, 3rd ed., 20, 95. 

Velocity-modulated allosteric regulation, V, ,-TYPE ALLOSTERIC SYSTEM VENOM EXONUCLEASE Venom phosphodiesterase, PHOSPHODIESTERASES VESICLE TRANSPORT IN CELLS Vibrational bond stretching mode,... 

Hemotoxic venoms of rattlesnakes and cottonmouths contain as their principal toxin phosphodiesterase, an enzyme that catalyzes hydrolysis ofphosphodiester bonds in ATP and other substrates. 

The question of enzyme specificity for irradiated polynucleotides is taken up in more detail in the recent review of Johns.11 The specificities of four enzymes, spleen phosphodiesterase, snake venom phosphodiesterase, pancreatic ribonuclease, and pancreatic deoxyribonuclease are discussed. 

The existence of photoreversible, but not of heat-reversible, absorbance change in irradiated poly dI dC was taken to prove that the photoproducts are entirely dimers (in contrast to those in poly C irradiations where the product is almost entirely the hydrate82a). It was possible to detect dimers of uracil as well as those of cytosine, by means of the much slower photoreversal of uracil dimers. In the acid hydrolysates of irradiated dl-dC, both uracil dimers and uracil could be identified. Enzymatic hydrolysis (snake venom phosphodiesterase) does not split pyrimidine dimers, and the products of such hydrolysis of irradiated tritium-labeled poly dl dC contained trinucleotides shown by radioactivity to contain cytosine dimers. Thymine dimers were formed in the photolysis of the poly dA dT, and were detected and assayed by the same methods. The yield of thymine dimers in irradiated poly... 

Apart from important similarities in the endo- and exonucleolytic properties of staphylococcal nuclease and other well-studied phosphodiesterases (67), those from snake venom and spleen, the basic structural substrate elements for these enzymes appear to be quite different... 

Fig. 2. Proposed structural requirements for substrates of phosphodiesterases that hydrolyze DNA and RNA, those from (a) snake venom, (b) spleen, and (c) staphylococcus (R = thymine and R — p-nitrophenyl). The studies indicated for the venom and spleen enzymes are those suggested by Khorana (67) [data from Cuatrecasas el al. (61)).

First, exonuclease (phosphodiesterase), endonuclease (8, 10-12), 5 -nucleotidase (13), and nonspecific phosphatase (13) are present in all venoms that have been analyzed. Therefore, nature did not provide these materials as sources of any one of these enzymes free from undesirable contaminants which may be represented by the others. 

The terms venom exonuclease and venom phosphodiesterase are at present used interchangeably to designate the same enzyme. The reviewer prefers the first, because he would like to see phosphodiesterase restored to it original meaning as the general name for all enzymes attacking diesterified phosphate. During the recent past, venom exonuclease has been reviewed several times (15-21). Three books (22-24) devoted to nucleases discuss venom exonuclease. 

Other substrates for spleen exonuclease are the p-nitrophenyl esters of nucleoside-3 -phosphates and bis(p-nitrophenyl) phosphate, which is split only very slowly. These substrates are also split by enzymes having quite different natural substrates (Table I) (80-87). In fact, not only phosphodiesterases, in a broad sense, such as acid DNase, micrococcal nuclease, spleen and venom exonucleases, and cyclic phosphodiesterase but also enzymes such as nucleoside phosphoacyl hydrolase and nucleoside polyphosphatase split these substrates. As pointed out by Spahr and Gesteland (86), this may be explained by the fact that these substrates are not true diesters but rather mixed phosphoanhydrides because of the acidic character of the phenolic OH. It is evident that the use of the synthetic substrates, advocated by Razzell (3) as specific substrates for exonucleases, may be very misleading. Table II shows the distinctive characters of three spleen enzymes active on bis(p-nitrophenyl) phosphate which are present in the crude extracts from which acid exonuclease is prepared. 

In addition to the proposed regulatory role of ATP and pyrophosphate, some possibility exists that 3, 5 -cyclic phosphate diesterase is under physiological control. Such ideas arose through observations of Cheung (43, 62) that the partially purified enzyme from beef brain was markedly activated by snake venom. The stimulatory factor was labile at extreme pH it was not dialyzable and appeared to be a protein. A similar activating factor is also present in brain tissue (63) and is removed during purification of the diesterase. It seems to interact stoichiometrically with the enzyme. The activator is destroyed by trypsin and is not proteolytic itself. The precise role of this protein in regulating the phosphodiesterase in vivo is not yet established, however. 

When the Tg lesions is opened by ammonolysis, the resulting product (ureidoisobutyric acid) inhibits snake venom phosphodiesterase, A exonuclease and the Klenow (exo ) fragment (Matray et al. 1995 see also Greenberg and Matray 1997). It is, however, removed by E. coli Fpg and Nth proteins (Jurado et al. 1998). 

All three of the fully-unblocked dodecamers underwent complete digestion to give their monomeric components when they were treated with Crotalus adamanteus snake venom and spleen phosphodiesterases. Their structures were further confirmed in the usual way. 

SVPDE/AP snake venom phosphodiesterase and alkaline phosphatase t-BOC tm-butoxycarbonyl (group)... 

Snake Venom Phosphodiesterase An exonuclease is an enzyme that sequentially cleaves nucleotides from the end of a polynucleotide strand. Snake venom phosphodiesterase, which hydrolyzes nucleotides from the 3 end of any oligonucleotide with a free 3 -hydroxyl group, cleaves between the 3 hydroxyl of the ribose or deoxyribose and the phosphoryl group of the next nucleotide. It acts on single-stranded DNA or RNA and has no base specificity. This enzyme was used in sequence... 

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