Raman spectroscopy of interferon-induced 2',5'-linked oligoadenylates

Raman spectra of model compounds and of 2',5'-oligoadenylates in D2O were utilized to assign the Raman bands of 2',5'-oligoadenylates. The Raman spectra of A2'pA2'pA, pA2'pA2'pA, and pppA2'pA2'pA contained features that were similar to those of adenosine, adenosine 5'-monophosphate (AMP), and adenosine 5'-triphosphate, respectively. When AMP and pA2'pA2'pA were titrated from pH 2 to 9, the normalized Raman intensity of their ionized (980 cm-1) and protonated (1080 cm-1) phosphate bands revealed similar pKa's for the 5'-monophosphates. The Raman spectrum of pA2'pA2'pA was altered slightly by elevations in temperature, but not in a manner supporting the postulate that 2-5A possesses intermolecular base stacking. Major differences in the Raman spectrum of 2',5'- and 3',5'-oligoadenylates were observed in the 600-1200-cm-1 portion of the spectrum that arises predominately from ribose and phosphate vibrational modes. Phosphodiester backbone modes in A3'pA3'pA and pA3'pA3'pA produced a broad band at 802 cm-1 with a shoulder at 820 cm-1, whereas all 2',5'-oligoadenylates contained a major phosphodiester band at 823 cm-1 with a shoulder at 802 cm-1. The backbone mode of pppA2'pA2'pA contained the sharpest band at 823 cm-1, suggesting that the phosphodiester backbone may be more restrained in the biologically active, 5'-triphosphorylated molecule. The Raman band assignments for 2',5'-oligoadenylates provide a foundation for using Raman spectroscopy to explore the mechanism of binding of 2',5'-oligoadenylates to proteins.     

Spectrophotometric assay, solubilization and purification of brain 2'':3''-cyclic nucleotide 3''-phosphodiesterase.

1. A spectrophotometric assay of 2':3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37) based on the use of an acid-base indicator and a buffer having identical pKa values is described. The assay is simple and rapid; it was particularly convenient for monitoring the enzyme activity at various stages of purification. 2. Several proteinases were examined for their ability to solubilize 2':3'-cyclic nucleotide 3'-phosphodiesterase from delipidated brain white matter. Trypsin (EC 3.4.21.4) and elastase (EC 3.4.21.11) appeared to be more effective than the other proteinases examined. Trypsin, however, caused inactivation; elastase was therefore chosen to solubilize 2':3'-cyclic nucleotide 3'-phosphodiesterase. When a partially purified preparation of 2':3'-cyclic nucleotide 3'-phosphodiesterase was treated with elastase, 2':3'-cyclic nucleotide 3'-phosphodiesterase was solubilized nearly quantitatively. Elastatinal, a specific inhibitor of elastase, specifically inhibited the solubilization with elastase. 3. 2':3'-cyclic nucleotide 3'-phosphodiesterase was purified from bovine brain white matter by: (i) delipidation; (ii) solubilization with hexadecyltrimethylammonium bromide; (iii) gel chromatography on Sepharose; (iv) ethanol precipitation and resolubilization by digestion with elastase; (v) chromatography on DEAE-Sephadex; (vi) affinity chromatography on 8-(6-aminohexyl)amino-2'-AMP-Sepharose. 4. The purified enzyme migrated as a single protein band on polyacrylamide-gel electrophoresis at pH 4.3 and on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis; the estimated mol.wt. in the latter electrophoresis was 27000-31000. Gel filtration of the purified enzyme through Sephadex G-150 indicated a mol.wt. of 31000. Therefore the purified enzyme is a monomer protein with a mol.wt. of approx. 30000.     

Regulation of poly(ADP-ribose) transferase activity by 2',5'-oligoadenylates

pppA2'pA2'pA appears to be a potent natural noncompetitive inhibitor of poly (ADP-ribose) transferase activity in the histone dependent reaction of ADP-ribosylation with Ki=5 microM. Moreover, it is a noncompetitive inhibitor of the Mg2+ dependent reaction of autoADPRT-ribosylation with Ki=20 microM. The activity of ADPRT falls down abruptly both in the cytoplasm and nuclei of mouse L-cells treated with interferon. In contrast, the activities of 2',5'-oligo (A) polymerase and 2'-phosphodiesterase remain virtually unchanged after the treatment with ADPRT preparation. The regulation of ADPRT activity and active form of ADPRT by 2',5-oligoadenylates is presumed to be one of the factors responsible for inducing the antiviral and/or antiproliferative effects of interferon.     

Kinetics and activation parameter analyses of hydrolysis and interconversion of 2',5'- and 3',5'-linked dinucleoside monophosphate at extremely high temperatures

Kinetic analysis of hydrolytic stability of 2',5'- and 3',5'-linked dinucleoside monophosphate (N(2)'pN and N(3)'pN) was successfully performed in aqueous solution at 175-240 degrees C using a new real-time monitoring method for rapid hydrothermal reactions. The half-lives of NpN were in the range 2-8 s at 240 degrees C and apparent activation energy decreases in the order U(2)'pU>A(2)'pA>G(2)'pG>U(3)pU approximately C(3)'pC>A(3)pA. The stability of phosphodiester bond was dependent on the types of base moiety and phosphodiester linkages, but no systematic correlation was found between the structure and stability. The interconversion of 2',5'-adenylyladenosine monophosphate (A(2)'pA) and 3',5'-adenylyladenosine monophosphate (A(3)'pA) was enhanced in the presence of D- or L-histidine. The rate constants of degradation of NpN were dissected into the rate constants of hydrolysis and interconversion between N(2)'pN and N(3)'pN using a computer program SIMFIT. Kinetic analysis supports the mechanism that imidazolium ion and imidazole catalyze interconversion and hydrolysis even under hydrothermal environments. The activation parameters for the hydrolysis and interconversion of NpN were systematically determined for the first time from the temperature dependence of the rate constants, where both DeltaH(app)( not equal ) and DeltaS(app)( not equal ) for 2',5'-linked NpN are larger than those for 3',5'-linked NpN. These parameters support the pseudorotation mechanism through pentacoordinate intermediate from 2',5'- and 3',5'-linked NpN, where the average value of DeltaH( not equal ) (pseudorotation) was estimated to be 30+/-18 kJ mol(-1) at 175-240 degrees C.     

Separation and identification of 2',3'-cyclic nucleotide 3'-phosphodiesterase on isoelectric focusing gels

A method is presented for the separation and detection of the myelin marker enzyme 2',3'-cyclic nucleotide 3'-phosphodiesterase on isoelectric focusing gels and by immunoblotting. The gel staining procedure is a modification of a method used to demonstrate enzyme activity on blots after sodium dodecyl sulfate-polyacrylamide gel electrophoresis and two-dimensional polyacrylamide gel electrophoresis. The results show that immunologically active 2',3'-cyclic nucleotide 3'-phosphodiesterase can be separated under equilibrium conditions on isoelectric focusing gels with an expanded alkaline pH range after solubilization in a mixture of nonionic/zwitterionic detergents and urea. Enzymatically active 2',3'-cyclic nucleotide 3'-phosphodiesterase focused as two closely spaced bands at pIapp 8.1 and 8.8, respectively, while 2',3'-cyclic nucleotide 3'-phosphodiesterase immunoreactivity was detected as four distinct bands at pIapp 4.2, 7.4, 8.8, and 9.3 and a diffuse band at pIapp 7.9-8.2. By two-dimensional separation these five bands showed molecular weights of about 43-47 kDa, i.e., corresponding to reported values for immunologically active 2',3'-cyclic nucleotide 3'-phosphodiesterase. Since enzyme activity is associated with only two of the bands, nonspecific and artifactual banding due to, e.g., detergent micelle formation, is unlikely.     

Affinity purification and properties of cathepsin-E-like acid proteinase from rat spleen.

A unique acid proteinase different from cathepsin D was purified from rat spleen by a method involving precipitation at pH 3.5, affinity chromatography on pepstatin-Sepharose 4B and concanavalin A-Sepharose 4B, chromatography on Sephadex G-100 and DEAE-Sephacel, and isoelectric focusing. A purification of 4200-fold over the homogenate was achieved and the yield was 11%. The purified enzyme appeared to be homogeneous on electrophoresis in polyacrylamide gels. The isoelectric point of the enzyme was determined to be 4.1-4.4. The enzyme hydrolyzed hemoglobin with a pH optimum of about 3.1. The molecular weight of the enzyme was estimated to be about 90000 by gel filtration on Sephadex G-100. In sodium dodecylsulfate polyacrylamide gel electrophoresis, the purified enzyme showed a single protein band corresponding to a molecular weight of about 45000. The hydrolysis of bovine hemoglobin by the enzyme was much higher than that of serum albumin. Various synthetic and natural inhibitors of the enzyme were tested. The enzyme was inhbited by Zn2+, Fe3+, Pb2+, cyanide, p-chloromercuribenzoate, iodoacetic acid and pepstatin, whereas 2-mercaptoethanol, phenylmethyl-sulfonyl fluoride and leupeptin showed no effect.     

Diastereomeric specificity of 2',3'-cyclic nucleotide 3'-phosphodiesterase.

The diastereomers of adenosine and uridine 2',3'-cyclic phosphorothioates were tested as substrates for 2',3'-cyclic nucleotide 3'-phosphodiesterase from bovine brain. The enzyme cleaves the Sp (or exo) diastereomers efficiently, whereas the Rp (or endo) diastereomers are resistant to hydrolysis, even after long incubation. As the enzyme exhibits strong substrate inhibition the precise determination of kinetic parameters posed problems, particularly with phosphorothioates. The stereoselectivity of this enzyme is opposite to that of RNase T1 and RNase A and thus could be a useful complement in determination of the configuration of nucleoside 2',3'-cyclic phosphorothioates resulting from hydrolysis reactions of unknown stereochemical course.     

A misaligned double-stranded RNA, poly(I).poly(C12,U), induces accumulation of 2',5'-oligoadenylates in mouse tissues

2',5'-Oligoadenylate synthetase was induced 3-2000-fold in spleen, liver, kidney and brain of NIH Swiss mice injected intravenously with 2-200 micrograms of the misaligned dsRNA, poly(I).poly(C12,U). Levels of 2',5'-oligoadenylates extracted from these tissues were also elevated, although the amount of 2',5'-oligoadenylates extracted did not correlate directly with the amount of enzyme present. These results suggest that double-stranded portions of the misaligned polymer survived intracellularly and activated the 2',5'-oligoadenylate synthetase, and that the level of dsRNA may contribute to the control of 2',5'-oligoadenylate metabolism.     

Purification and characterization of an apurinic/apyrimidinic endonuclease from HeLa cells

An endodeoxyribonuclease from HeLa cells acting on apurinic/apyrimidinic (AP) sites has been purified to apparent homogeneity as judged by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. The presence of Triton X-100 was necessary throughout the purification for stabilization and stimulation of activity. The endonuclease has an apparent native molecular weight of 32,000 determined by molecular sieving and an apparent subunit molecular weight of 41,000 as judged by its electrophoretic mobility in SDS-polyacrylamide gels. The activity has an absolute requirement for Mg2+ or Mn2+ and a broad pH optimum between 6.7 and 9.0 with maximal activity near pH 7.5. The enzyme has no detectable exonuclease activity, nor any endonuclease activity on untreated duplex or single-stranded DNA. It is inhibited by adenine, hypoxanthine, adenosine, AMP, ADP-ribose, and NAD+, but it is unaffected by caffeine, the pyrimidine bases, ADP, ATP, or NADH. The use of a variety of damaged DNA substrates provided no indication that the enzyme acts on other than AP sites. The enzyme appears to cleave AP DNA so as to leave deoxyribose-5-phosphate at the 5' terminus and a 3'-OH at the 3' terminus; it also removes deoxyribose-5-phosphate from AP DNA which has deoxyribose at the 3' terminus. Specific antibody has been produced in rabbits which interacts only with a 41,000-dalton protein present in the purified enzyme (presumably the enzyme itself), as well as with partially purified AP endonuclease fractions from human placenta and fibroblasts.     

cDNA cloning and amino acid sequence of bovine brain 2',3'-cyclic-nucleotide 3'-phosphodiesterase

2',3'-Cyclic-nucleotide 3'-phosphodiesterase (EC 3.1.4.37) has been widely used as a marker for myelin-oligodendrocytes in the central nervous system. Evidence has been provided that the enzyme is identical with one of the Wolfgram proteins of central nervous system myelin. The amino acid sequence of bovine 2',3'-cyclic-nucleotide 3'-phosphodiesterase was determined by both protein and cDNA sequence analyses. Protein sequence analysis was done on bovine elastase 2',3'-cyclic-nucleotide 3'-phosphodiesterase, a low molecular weight enzyme obtained by solubilization with pancreatic elastase (EC 3.4.21.36) (Nishizawa, Y., Kurihara, T., and Takahashi, Y. (1980) Biochem. J. 191, 71-82; Kurihara, T., Nishizawa, Y., Takahashi, Y., and Odani, S. (1981) Biochem. J. 195, 153-157). Based on the carboxyl-terminal sequence of bovine elastase 2',3'-cyclic-nucleotide 3'-phosphodiesterase, synthetic oligodeoxyribonucleotides were prepared and used as probes for screening a cDNA library of bovine brain. A cDNA of 2305 base pairs was obtained and sequenced, and the complete amino acid sequence of bovine 2',3'-cyclic-nucleotide 3'-phosphodiesterase was deduced. Bovine 2',3'-cyclic-nucleotide 3'-phosphodiesterase deduced contains 400 amino acids including initiation methionine and has a molecular weight of 44,850. Bovine elastase 2',3'-cyclic-nucleotide 3'-phosphodiesterase corresponds to the 236 amino acids of bovine 2',3'-cyclic-nucleotide 3'-phosphodiesterase. RNA blot analysis revealed a single-species mRNA of about 2600 bases.     

Purification and characterization of wheat germ 2',3'-cyclic nucleotide 3'-phosphodiesterase

The 2',3'-cyclic nucleotide 3'-phosphodiesterase which hydrolyzes nucleoside 2',3'-cyclic phosphates (N greater than p) to nucleoside 2'-phosphates has been purified 16,000-fold to near homogeneity from wheat germ. The purified enzyme is a single polypeptide with a molecular weight of 23,000-24,000. It has a pH optimum of 7.0. The apparent Km values for A greater than p, G greater than p, C greater than p, and U greater than p are 13.1, 9.2, 25.2, and 25.3 mM, respectively. Vmax values for A greater than p, G greater than p, C greater than p, and U greater than p are 2090, 280, 2140, and 600 mumol/min/mg of purified protein, respectively. Wheat germ 2',3'-cyclic nucleotide 3'-phosphodiesterase does not hydrolyze 2',3'-cyclic esters in cyclic phosphate-terminated oligoribonucleotides or in nucleoside 5'-phosphate, 2',3'-cyclic phosphate (pN greater than p). This is in contrast to the 3'-phosphodiesterase activity associated with a wheat germ RNA ligase which hydrolyzes cyclic phosphate-terminated oligonucleotides and pN greater than p substrates much more efficiently than nucleoside 2',3'-cyclic phosphates. The enzyme characterized in this work appears to be the only known 2',3'-cyclic nucleotide 3'-phosphodiesterase specific for 2',3'-cyclic mononucleotides.     

Phenobarbital enhances 2',5'-oligoadenylate synthesis in rat liver nuclei

Treatment of rats with phenobarbital for three days greatly increases the activity of 2,5 oligoadenylate synthetase in liver nuclei. Analysis of 2',5'-oligoadenylates synthesized in vitro showed that nuclei from both phenobarbital-treated and control rats synthesized 2',5'-oligoadenylates ranging from di- to hexamers. However, nuclei from drug treated rats showed a two fold increase in trimer and tetramer synthesis and a three-four fold increase in longer chained oligoadenylates. There was no change in the nuclear 2'-phosphodiesterase activity as the result of phenobarbital treatment, This activity remained low in nuclei from either the treated or the control rats. To our knowledge, this is the first report on phenobarbital affecting the liver 2',5'-oligoadenylate system.     

Human 2'-phosphodiesterase localizes to the mitochondrial matrix with a putative function in mitochondrial RNA turnover

The vertebrate 2-5A system is part of the innate immune system and central to cellular antiviral defense. Upon activation by viral double-stranded RNA, 5'-triphosphorylated, 2'-5'-linked oligoadenylate polyribonucleotides (2-5As) are synthesized by one of several 2'-5'-oligoadenylate synthetases. These unusual oligonucleotides activate RNase L, an unspecific endoribonuclease that mediates viral and cellular RNA breakdown. Subsequently, the 2-5As are removed by a 2'-phosphodiesterase (2'-PDE), an enzyme that apart from breaking 2'-5' bonds also degrades regular, 3'-5'-linked oligoadenylates. Interestingly, 2'-PDE shares both functionally and structurally characteristics with the CCR4-type exonuclease-endonuclease-phosphatase family of deadenylases. Here we show that 2'-PDE locates to the mitochondrial matrix of human cells, and comprise an active 3'-5' exoribonuclease exhibiting a preference for oligo-adenosine RNA like canonical cytoplasmic deadenylases. Furthermore, we document a marked negative association between 2'-PDE and mitochondrial mRNA levels following siRNA-directed knockdown and plasmid-mediated overexpression, respectively. The results indicate that 2'-PDE, apart from playing a role in the cellular immune system, may also function in mitochondrial RNA turnover.     

A rapid method for the purification of glucose-6-phosphate dehydrogenase from bovine lens.

This paper describes a simple and rapid method for the purification of glucose-6-phosphate dehydrogenase from bovine lens, together with analysis of the kinetic behaviour and some properties of the enzyme. The purification consisted of two steps, 2',5'-ADP-Sepharose 4B affinity chromatography and DEAE Sepharose Fast Flow ion exchange chromatography in procedure which took two working days. The enzyme was obtained with a yield of 13.7% and had a specific activity of 2.64 U/mg protein. The overall purification was about 19,700-fold. The molecular weight of the enzyme was found to be 62 +/- 3 kDa by Sephadex G-200 gel filtration chromatography. A protein band corresponding to a molecular weight of 69.2 +/- 3.2 kDa was obtained on SDS polyacrylamide slab gel electrophoresis. On chromatofocusing, lens glucose-6-phosphate dehydrogenase gave a single peak at pI 5.14. The activation energy of the reaction catalyzed by the enzyme was calculated from Arrhenius plot as Ea = 5.88 kcal/mol. The pH versus velocity curve had two peaks at pH 7.7 and 9.6. By the double-reciprocal plots and the product inhibition studies, it was shown that the enzyme follows 'Ordered Bi Bi' sequential kinetics. From the graphical and statistical analyses, KmNADP+, KmG-6-P, KiNADPH, Ki6-PGA were estimated to be 0.008 +/- 0.002, 0.035 +/- 0.013, 0.173 +/- 0.007 and 1.771 +/- 0.160 mM, respectively. The observed kinetic behaviour of glucose-6-phosphate dehydrogenase from bovine lens was in accordance with the enzyme from other sources.     

Inhibition of bovine and human brain 2':3'-cyclic nucleotide 3'-phosphodiesterase by heparin and polyribonucleotides and evidence for an associated 5'-polynucleotide kinase activity

The present paper establishes a 5'-polynucleotide kinase activity associated with the bovine and human brain enzyme 2':3'-cyclic nucleotide 3'-phosphodiesterase (EC 3.1.4.37) in addition to known extremely high hydrolysis rates against 2':3'-cyclic nucleotides. Modulation of the enzyme activity by the addition of polyadenylate (5') and polyuridylate (5'), histone F3, myelin basic protein (MBP), and other basic molecules suggest that RNA may be the natural substrate for both enzymes. These enzymes, isolated from brain and present in very high activities in oligodendrocytes and in isolated myelin, probably have complex functions.     

Purification and characterization of cytoplasmic 5'(3')-nucleotidase from rabbit spleen: characteristic differences of the enzyme from the rat spleen nucleotidase.

1. A 5'(3')-nucleotidase, which preferably hydrolyzed 3'-dTMP and 3'-dUMP, was highly purified from rabbit spleen cytosol. 2. The enzyme also hydrolyzes 3'-UMP, 5'-dUMP and guanine nucleotides, but does not hydrolyze any adenine nucleotides or cytosine nucleotides. 3. The activity is dependent upon Mg2+, Co2+ or Mn2+; the addition of deoxyinosine stimulates the activity, and the pH optimum for the hydrolysis of 3'-dTMP is 7.0. 4. Although the catalytic properties of the enzyme are similar to the 5'(3')-nucleotidase from rat spleen, these nucleotidases differ in their molecular disposition. 5. The charge state of the rabbit enzyme is slightly basic, and the subunit M(r) is about 27 kDa, while the value of the rat enzyme is 26 kDa. 6. Immunochemical experiments with the use of antibodies against the purified nucleotidase indicate that enzymes from rabbit spleen and from rat spleen are composed of different polypeptides.     

Isolation and properties of an extracellular beta-glucosidase from the polycentric rumen fungus Orpinomyces sp. strain PC-2.

An extracellular beta-glucosidase (EC 3.2.1.21) was purified from culture filtrate of the anaerobic rumen fungus Orpinomyces sp. strain PC-2 grown on 0.3% (wt vol-1) Avicel by using Q Sepharose anion-exchange chromatography, ammonium sulfate precipitation, chromatofocusing ion-exchange chromatography, and Superose 12 gel filtration. The enzyme is monomeric with a M(r) of 85,400, as estimated by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, has a pI of 3.95, and contains about 8.5% (wt vol-1) carbohydrate. The N terminus appears to be blocked. The enzyme catalyzes the hydrolysis of cellobiose and p-nitrophenyl-beta-D-glucoside (PNPG). The Km and Vmax values with cellobiose as the substrate at pH 6.0 and 40 degrees C are 0.25 mM and 27.1 mumol.min-1 x mg-1, respectively; with PNPG as the substrate, the corresponding values are of 0.35 mM and 27.7 mumol.min-1 x mg-1. Glucose (Ki = 8.75 mM, with PNPG as the substrate) and gluconolactone (Ki = 1.68 x 10(-2) and 2.57 mM, with PNPG and cellobiose as the substrates, respectively) are competitive inhibitors. Optimal activity with PNPG and cellobiose as the substrates is at pH 6.2 and 50 degrees C. The enzyme has high activity against sophorose (beta-1,2-glucobiose) and laminaribiose (beta-1,3-glucobiose) but has no activity against gentiobiose (beta-1,6-glucobiose). The activity of the beta-glucosidase is stimulated by Mg2+, Mn2+, Co2+, and Ni2+ and inhibited by Ag+, Fe2+, Cu2+, Hg2+, SDS, and p-chloromercuribenzoate.     

Purification by affinity chromatography of 2,4-dienoyl-CoA reductases from bovine liver and Escherichia coli

1. Dye-ligand chromatography using immobilized Cibacron blue F3GA (blue Sepharose CL-6B) and Procion red HE3B (Matrex gel red A) as matrices and general ligand chromatography employing immobilized 2',5'-ADP (2',5'-ADP-Sepharose 4B) and immobilized 3',5'-ADP (3',5'-ADP-Agarose) were employed for purification of NADPH-dependent 2-enoyl-CoA reductase and 2,4-dienoyl-CoA reductase from bovine liver (formerly called 4-enoyl-CoA reductase [Kunau, W. H. and Dommes, P. (1978) Eur. J. Biochem. 91, 533-544], as well as 2,4-dienoyl-CoA reductase from Escherichia coli. 2. The NADPH-dependent 2-enoyl-CoA reductase from bovine liver mitochondria was separated from 2,4-dienoyl-CoA reductase by dye-ligand chromatography (Matrex gel red A/KCl gradient) as well as by general ligand affinity chromatography (2',5'-ADP-Sepharose 4B/NADP gradient). The enzyme was obtained in a highly purified form. 3. The NADPH-dependent 2,4-dienoyl-CoA reductase from bovine liver mitochondria was purified to homogeneity using blue Sepharose CL-6B, Matrex gel red A, and 2',5'-ADP-Sepharose 4B chromatography. 4. The bacterial 2,4-dienoyl-CoA reductase was completely purified by ion-exchange chromatography on DEAE-cellulose followed by a single affinity chromatography step employing 2',5'-ADP-Sepharose 4B and biospecific elution from the column with a substrate, trans,trans-2,4-decadienoyl-CoA. 5. The application of dye-ligand and general ligand affinity chromatography for purification of NADPH-dependent 2,4-dienoyl-CoA reductases taking part in the beta-oxidation of unsaturated fatty acids is discussed. It is concluded that making use of coenzyme specificity for binding and substrate specificity for elution is essential for obtaining homogeneous enzyme preparations.     

A nucleotide phosphodiesterase with preference for 2',5'-phosphodiester bonds from Ehrlich ascites carcinoma

We have previously reported that many tumor cell lines express a 5'-nucleotide phosphodiesterase (phosphodiesterase I, EC 3.1.4.1) with properties clearly distinguishable from enzymes of normal tissues (Biochim. Biophys. Acta (1988) 966, 99-106). Such an enzyme with 5'-nucleotide phosphodiesterase activity was purified from Ehrlich ascites carcinoma by measuring the cleavage of thymidine 5'-monophosphate p-nitrophenyl ester (TMP-NP). The enzyme is a soluble protein, has a pH optimum of 7.5, and the molecular mass estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis is 67 kDa. The enzyme does not hydrolyze other chromogenic substrates for phosphodiesterases, nor pyrophosphate bond of various nucleotides which are cleaved by 5'-nucleotide phosphodiesterases of normal tissues. But, it hydrolyzes dinucleotides to form 5'-phosphates, and is more active on 2',5'- than on 3',5'-phosphodiester bonds. These results indicate that the TMP-NP splitting enzyme in Ehrlich ascites carcinoma cells is a 2',5'-phosphodiesterase.     

Isolation of a 5.3-S calmodulin-deficient 3'':5''-cyclic nucleotide phosphodiesterase from cardiac muscle.

1. In the presence of Ca2+, a 5.3-S 3':5'-cyclic nucleotide phosphodiesterase (EC 3.1.4.17) from bovine ventricle was isolated and purified by (NH4)2SO4 precipitation and DEAE-cellulose and Affi-Gel Blue chromatography. The enzyme activity was enriched 800-fold by these procedures. 2. Sucrose-density gradient centrifugation, gel filtration and non-denaturing polyacrylamide-gel electrophoresis resolved a single enzyme species with an Mr of 89 000. 3. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis of the purified enzyme demonstrated a prominent protein band at Mr 59000 and a minor band of Mr 28000. Calmodulin was not detected. 4. The hydrolysis of micromolar concentrations of 3':5'-cyclic guanosine monophosphate (cyclic GMP) but not 3':5'-cyclic adenosine monophosphate (cyclic AMP) was stimulated by calmodulin. 5. Anomalous biphasic kinetics plots were observed for both the catalysis of cyclic AMP and cyclic GMP hydrolysis. Kinetic plots became linear in the presence of calmodulin. 6. After several months of storage at -20 degrees C, the 5.3-S enzyme was transformed into a 6.2-S cyclic GMP-specific enzyme and a 4.4-S non-specific form.