Changes in polypeptide synthesis and glycosylation in mouse embryonic fibroblast C3H/10T1/2 Cl 8 cells caused by the tumor promoter 12-O-tetradecanoylphorbol 13-acetate

The mechanism of tumor promotion is not well understood. We have used the transformable, tumor promotable, mouse embryo fibroblast C3H/10T1/2 Cl 8 cells to study tumor promoter specific changes in protein synthesis and protein glycosylation. Two-dimensional gel electrophoresis showed that 12-O-tetradecanoylphorbol 13-acetate caused a significant increase in the synthesis of five cellular and 34 extracellular polypeptides. One of these polypeptides has tentatively been identified as ornithine decarboxylase. One new polypeptide (p 62, Mr 58,000) was found in the medium of 12-O-tetradecanoylphorbol 13-acetate-treated cells. The amounts of several excreted proteins were enhanced 5-10 fold by 12-O-tetradecanoylphorbol 13-acetate. 12-O-tetradecanoylphorbol 13-acetate interfered with glycosylation both by affecting protein synthesis and also directly with glycosylation. At least 15 polypeptides in the medium and two cellular polypeptides decreased after 12-O-tetradecanoylphorbol 13-acetate treatment. Two of the major polypeptides found in the medium (p 8 and 10, Mr approx. 200,000-220,000) have properties similar to fibronectin, while p 9 and 11 both found in the cellular preparations and in the medium (Mr 180,000 and 150,000) were collagenase sensitive and their synthesis was inhibited by 12-O-tetradecanoylphorbol 13-acetate.

Enhanced expression of c-myc and decreased expression of c-fos protooncogenes in chemically and radiation-transformed C3H/10T1/2 Cl 8 mouse embryo cell lines

c-abl, c-fos, c-Ha-ras, c-myc, and c-mos were expressed whereas c-sis, c-fms, c-rel, c-src, and c-myb expression was not detectable in C3H/10T1/2 Cl 8 (10T1/2) cells and in eight chemically and radiation-transformed 10T1/2 cell lines. The expression of c-abl, c-fos, c-Ha-ras, and c-myc was growth-related in nontransformed 10T1/2 cells. c-abl and c-fos expression increased at confluence by 5- and 9-fold, respectively, compared to that in log phase cells. c-Ha-ras and c-myc transcripts were most abundant in log phase cells and decreased by 70 and 50%, respectively, in confluent cells. There were no significant growth-related changes in the expression of c-Ha-ras, c-myc, or c-abl in methylcholanthrene-transformed Cl 15 cells. The c-fos transcript was not detected in Cl 15 cell cultures. c-abl, c-fos, c-ras, and c-myc were expressed in whole C3H mouse embryo tissue, mouse liver, and 10T1/2 cells. Sizes of these protooncogene transcripts in 10T1/2 cells were the same as those in whole embryo tissue, except that 10T1/2 cells did not express the 8.2-kilobase abl transcript. At subconfluence, equivalent low levels of c-mos expression were observed in nontransformed and in the eight transformed 10T1/2 cell lines. The level of c-abl expression was similar in the nontransformed and in the eight transformed cell lines, but there was a new 8.2-kilobase transcript in the transformed MCA Cl 15 cell line. c-fos was expressed in 10T1/2 cells but was not detectable or greatly reduced in eight transformed cell lines. c-Ha-ras was expressed to a similar extent in eight transformed cell lines and in nontransformed 10T1/2 cells. In the UVC-4 transformed cell line, extra 3.3-kilobase Ha-ras and 7.5-kilobase Ki-ras transcripts were observed. c-myc was expressed at 4- to 7-fold higher levels in six transformed cell lines compared to 10T1/2 cells. There were no major rearrangements in or amplification of the c-myc gene in three transformed cells overexpressing this gene 5-fold. These studies show that enhanced expression of c-myc and decreased expression of c-fos correlate with the chemically and radiation transformed states of 10T1/2 cells. Changes in c-fos and c-myc oncogene expression may be casually linked to late stages of neoplastic transformation in these chemically and radiation transformed 10T1/2 cell lines.

Differential effects of chlorpromazine on secretion, protein phosphorylation and phosphoinositide metabolism in stimulated platelets

Increasing concentrations of chlorpromazine (30-500 microM) caused a progressive lysis of gel-filtered platelets, as monitored by the extracellular appearance of cytoplasmic ([14C]adenine-labelled) adenine nucleotides. The chlorpromazine-induced lysis was markedly enhanced by thrombin and phorbol ester, and complete cytolysis was found at chlorpromazine concentrations of 100 microM and above in the presence of thrombin. At non-lytic concentrations, chlorpromazine caused a dramatic increase in the thrombin- or phorbol ester-mediated incorporation of 32P into phosphatidylinositol 4-phosphate and, to a lesser extent, into phosphatidylinositol 4,5-bisphosphate in platelets pulse-labelled with [32P]Pi. Chlorpromazine alone also caused an incorporation of 32P into the phosphoinositides. Non-lytic concentrations of chlorpromazine had no effect on the phosphorylation of the 47 kDa protein (regarded as the substrate for protein kinase C), but markedly inhibited the accompanying secretion of ATP + ADP and beta-hexosaminidase when platelets were incubated with 0.17 microM-phorbol ester or 0.1-0.2 unit of thrombin/ml. At lower concentrations of thrombin, chlorpromazine did not inhibit, but slightly enhanced, secretion. A protein of 82 kDa was phosphorylated during the interaction of platelets with thrombin and phorbol ester, and this phosphorylation was enhanced by chlorpromazine (non-lytic). These results suggest that the previously reported inhibition of protein kinase C by chlorpromazine is probably non-specific and due to cytolysis. However, since non-lytic concentrations of chlorpromazine inhibit secretion, but not protein kinase C, in platelets, activation of protein kinase C is not involved in the stimulation-secretion coupling, or chlorpromazine acts at a step after kinase activation. Possible mechanisms of this inhibition by chlorpromazine are discussed in the light of its effect on phosphoinositide metabolism and protein phosphorylation.

Disposition of endogenous homocysteine by mouse fibroblast C3H/10T1/2 Cl 8 and the chemically transformed C3H/10T1/2 MCA Cl 16 cells following methotrexate exposure

The tumorigenic cell line termed "MCA Cl 16" was derived from C3H/10T1/2 clone (Cl) 8 cells by chemical transformation in the presence of 3-methylcholanthrene [(MCA) CAS: 56-49-5]. Transformed (Cl 16) cells were more sensitive toward the cytotoxic effect of methotrexate (MTX) than their normal counterpart Cl 8 cells. The disposition of endogenous L-homocysteine (Hcy) was investigated in these two cell lines after MTX exposure. Both nonmalignant and transformed cells exported Hcy into the extracellular medium, and only small amounts were retained within the cells. The Hcy efflux from the malignant cells was markedly increased after MTX exposure (0.5-10 microM), and this effect was almost completely prevented by 5-formyl-tetrahydrofolate (THF), whereas treatment with thymidine plus hypoxanthine did not inhibit the MTX-dependent Hcy efflux. Cytotoxic concentration of MCA reduced rather than increased the Hcy efflux from these cells. High concentrations of MTX (greater than 10 microM) were required to increase the release of Hcy from nonmalignant cells. The enhancement of Hcy export from the malignant cells in the presence of MTX was not associated with cellular build-up of S-adenosyl-L-homocysteine (AdoHcy), indicating that the amount of intracellular Hcy was kept below the level required for inhibition or reversion of the AdoHcy hydrolase reaction. MTX-dependent Hcy efflux probably reflects cellular deficiency of 5-methyl-THF required for the salvage of Hcy to methionine and may therefore be a measure of lack of this reduced folate relative to the metabolic demand.

Peroxisome proliferators show tumor-promoting but no direct transforming activity in vitro

The chemically unrelated hypolipidemic drugs, tiadenol, niadenate, and clofibrate have been tested for carcinogenic and tumor-promoting potential in the C3H/10TI/2 C18 cell test system. None of these chemicals were carcinogenic, while both niadenate and clofibrate were active tumor promoters at micromolar concentrations. All 3 drugs induced the differentiation of C3H/10T1/2 C18 cells to adipocytes. This latter finding confirms previously observed effects of the tumor promoter TPA.

The tumour promoter 12-O-tetradecanoylphorbol-13-acetate increases the activities of some peroxisome-associated enzymes in in vitro cell culture

A study was conducted on the effects of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on peroxisomal enzyme activities in mouse embryo fibroblasts C3H/10T1/2 C18 cells and chemically transformed C3H/10T1/2 MCA16 cells. TPA is a potent tumour promoter and treatment with this compound of the two cell lines induced peroxisomal fatty acid beta-oxidation, carnitine acetyltransferase, palmitoyl-CoA hydrolase, and catalase activities after 240 h of treatment. Stimulation of the corresponding enzyme activities was dose-related and cycloheximide inhibited the TPA-induced enzyme activities, except that of carnitine acetyltransferase. The MCA16 cells appeared to be more sensitive than the C18 cells in inducing peroxisome-associated enzyme activities after TPA treatment. The activities of the microsomal marker, NADPH-cytochrome c reductase and the mitochondrial marker, glutamate dehydrogenase were not enhanced by TPA treatment. The results indicate that TPA has peroxisomal effects and may be classified as a peroxisome proliferator.

Tiadenol-mediated induction of peroxisomal enzymes in cultured C3H/10T1/2CL8 cells and in chemically transformed C3H/10T1/2 MCA16 cells

The levels of peroxisomal enzyme activities in cultured C3H/10T1/2 CL8 cells and in chemically transformed C3H/10T1/2 MCA16 cells were studied after treatment with tiadenol and niadenate, two hypolipidemic drugs which are both carcinogenic and cause peroxisome proliferation in vivo. Administration of these peroxisome proliferators to the cells resulted in large increases in specific palmitoyl-CoA hydrolase, carnitine acetyl-transferase, and catalase activities. A reproducible induction of cyanide-insensitive palmitoyl-CoA oxidative activity was observed 5 and 9 days after initiation of tiadenol treatment. Basal activity was 0.16 nmole/min/mg protein compared to 0.95 nmole/min/mg protein in cells treated with 18 microM tiadenol (cytotoxicity of about 25%) for 9 days. The enzyme activities were more increased in the transformed MCA 16 cells than in the non-transformed cells and the order of increase in enzyme activities was: niadenate greater than tiadenol. In non-transformed cells, the specific activity of palmitoyl-CoA hydrolase was enhanced approximately 2.1-fold within 4 days after tiadenol treatment. During this time period the enzyme activity was constant in untreated cells, but decreased during longer incubation periods. The enhancement of palmitoyl-CoA hydrolase, carnitine acetyl-transferase and catalase activities was dose-related over a concentration range of 2 to 20 microM tiadenol, depending on the enzyme assayed. Tiadenol concentrations above 10 microM were increasingly cytotoxic, while 18 microM niadenate had no toxic effect on the C3H/10T1/2 C18 cells. Moreover, the stimulation of the 3 enzyme activities by the peroxisome proliferators were inhibited by cycloheximide. Neither of the two cell lines contained any appreciable urate oxidase activity. The responses of these cells to hypolipidemic drugs show that they constitute a useful system for studies on the role of peroxisomes in lipid metabolism and the relationship between hypolipidemic activity and carcinogenic potential of these drugs.

In vitro transformation and tumor promotion studies of styrene and styrene oxide

The carcinogenic properties of styrene and styrene oxide were investigated using C3H/10T1/2C18 cells as a test system. In vitro transformation was not observed for either of the two chemicals; however, styrene oxide at three different concentrations enhanced the morphological transformation in the two-stage transformation assay. 0.1, 1 and 10 microM styrene oxide added twice weekly resulted in 32.4, 26.8 and 31.4 per cent of the dishes with one or more type III foci. Styrene and styrene oxide were only slightly toxic to the cells at the concentrations used. Styrene oxide did not affect the growth rate of the C3H/10T1/2 cells at 10 microM. However, 100 microM styrene oxide added to logarithmically growing cells caused a significant decrease in growth rate within 24 to 48 h. The tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate inhibited DNA synthesis approximately 60% 8 h after initiation of treatment. When styrene oxide at concentrations up to 100 microM was tested in a similar experiment, however, no significant effect was observed. Total RNA synthesis increased by 70% 1.5 h after initiation of treatment at 1 microM styrene oxide; this effect was not seen after 24 h. Styrene oxide at concentrations of 1 and 0.1 microM stimulated the incorporation of [3H]choline into cells by approximately 20% during a 2 h incubation, the major site of incorporation being the nuclear-associated endoplasmic reticulum.

Purification and kinetic properties of polynucleotide kinase from rat testes

Polynucleotide kinase (EC 2.7.1.78) has been purified from rat testes, and an approximately 2000-fold purification was obtained. The purified enzyme had an Mr of 38000 +/- 3800. The enzyme phosphorylated micrococcal nuclease-treated calf thymus DNA and (dT)10 while 5'-HO-tRNA was a very poor substrate. A certain degree of specificity towards purine-containing 5'-HO-nucleotides was observed. The polynucleotide kinase had an absolute requirement for a divalent cation. Both Mg2+ and Mn2+ could be used, but 10 mM MgCl2 gave optimal activity. The monovalent cations Na+, K+ and NH4+ all stimulated enzyme activity, and the optimal concentration was 0.1 M. The enzyme was inhibited by inorganic phosphate, pyrophosphate and sulphate. A 50% inhibition was obtained with 20, 0.3 and 2 mM, respectively. At 2 mM MgCl2, 1 mM spermine enhanced the enzyme activity 3-times. The apparent KATP was estimated to be 36 microM and KHO-DNA was found to be 2 microM.

Xeroderma pigmentosum: in vitro complementation of DNA repair endonuclease

The DNA repair endonuclease activity has been studied in several xeroderma pigmentosum (XP) cell lines of complementation groups A and C. phi X174 RFI DNA treated with u.v.-light or OsO4 was used as a substrate. All XP cells tested appeared to lack this enzyme compared to control cells. However, when extracts from complementation groups A and C were mixed, activity levels close to that of the control cells were found, clearly indicating that the two cell lines can complement each other with regard to the DNA repair endonuclease activity. The XP cells were found to contain normal levels of AP-endonuclease.

The nuclear-associated endoplasmic reticulum is an early target for the action of the tumor promoter 12-O-tetradecanoyl phorbol-13-acetate in C3H/10T1/2 fibroblasts

12-O-Tetradecanoyl-phorbol-13-acetate (TPA) had a dual effect on the cellular membranes of C3H/10T1/2 cells in that it caused both a stimulation of [3H]choline incorporation and an enhancement of the solubilization of choline from prelabelled cells. Subfractionation studies showed that the release of [3H]choline occurred almost exclusively from nuclear-associated endoplasmic reticulum. The release was dependent on the presence of Mg2+ and Ca2+, indicating an enzyme-mediated reaction. In vivo, TPA stimulated the incorporation of [3H]choline into all subcellular fractions. The data indicate that the nuclear-associated endoplasmic reticulum represents an early target for TPA action.

The specific appearance of a 65,000 dalton protein in the nuclear associated endoplasmic reticulum of Krebs II ascites cells early after treatment with the phorbol ester TPA

The protein compositions of subcellular fractions prepared from untreated and 12-O-tetradecanoyl phorbol-13-acetate (TPA)-treated Krebs II ascites cells were examined by SDS-polyacrylamide gel electrophoresis. After 6 h of TPA treatment a 65,000 dalton protein in the nuclear associated endoplasmic reticulum showed a 240% increase when compared with the untreated control cells. The amount of this protein was similar in both untreated and TPA-treated cells up to 4 h of in vitro incubation. Though present in all other subcellular fractions, the amount of the 65,000 dalton protein was the same in both untreated and TPA-treated cells. Small changes were also observed in the amounts of other proteins in the nuclear associated endoplasmic reticulum in TPA-treated cells. The possibility was tested that the increased amount of the protein may have represented increased ornithine decarboxylase activity in response to TPA treatment. The time dependent appearance of the enzyme in untreated and TPA-treated cells, however, and the behaviour and subcellular localization of the 65,000 dalton protein ruled out the possibility that this protein and ornithine decarboxylase are one and the same molecule.

The phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate and stimulation of 3H-choline incorporation into endoplasmic reticulum membranes and other subcellular fractions of Krebs II ascites cells during in vitro incubation

After transfer of Krebs II ascites cells from the mouse peritoneum to suspension culture addition of the phorbol ester 12-0-tetradecanoyl-phorbol-13-acetate (TPA) causes an early stimulation of 3H-choline incorporation into phosphatidylcholine (PC). Choline transport into the treated cells, however, was unaffected. Within 30 min of TPA treatment 3H-choline incorporation was almost 300% above the control level. During a 5 hr period of suspension culture the overall patterns of 3H-choline incorporation were similar in TPA-treated and control cultures though the rate was greatly accentuated by the presence of the phorbol ester. Incubation of cells with cycloheximide prior to incubation with TPA did not result in an inhibition of the TPA-directed 3H-choline incorporation. After 3 hr incubation with TPA there were large increases in radioactivity in all subcellular fractions. At 20 hr, however, the values were not far from those of the control. During the first 3 hr of incubation with TPA the incorporation of 3H-choline into light rough (LR) and smooth (S) membranes was stimulated to levels of 400% and 320% respectively above control values. At later times the profiles of radioactivity in membrane subfractions in TPA-treated and control cultures were similar. The results illustrate an early effect of TPA on PC biosynthesis in Krebs II ascites cells while at later times of incubation the stimulatory effect was virtually abolished.

Effect of diethylstilbestrol on the transformable mouse embryo fibroblast C3H/10T1/2C18 cells. Tumor promotion, cell growth, DNA synthesis, and ornithine decarboxylase

Transformable mouse embryo fibroblasts, C3H/10T1/2C18, have been used to study the carcinogenic effect of diethylstilbestrol (DES) in vitro. DES did not show any carcinogenic potential under standard assay conditions. Continuous treatment of the target cells for 5 weeks with 5 micro M DES resulted in 1 transformed focus from 32 dishes. However, DES was active as a co-carcinogen in the two-stage transformation assay at concentrations as low as 50 nM. Under identical conditions, 0.17 micro M 12-O-tetradecanoyl phorbol-13-acetate produced approximately twice as many transformed foci. DES was not toxic to the C3H/10T1/2C18 cells over a range of 0.05 to 5 micro M, and total DNA synthesis was not significantly altered up to 5 micro M DES. 1 micro M DES did not influence the doubling time of the C3H/10T1/2C18 cells. DES did not induce ornithine decarboxylase enzyme activity in this test system.

Effect of polyamines on enzymes involved in DNA repair

The influence of polyamines on various enzymes involved in the excision repair pathway of DNA, such as UV endonuclease, DNA polymerase I, DNA ligase and polynucleotide kinase, and two AP-endonucleases, were studied. The polymerizing activities of DNA polymerase I and polynucleotide kinase were found to be markedly affected by polyamines. In the former enzyme the effect can be attributed to the stabilization of the correct bihelical structure at the 3' end and in the latter case polyamines stabilize the polynucleotide kinase protein itself in the correct oligomeric structure. The effect of polyamines on the hydrolysis of apurinic and apyrimidinic sites in DNA and nucleosome particles were also investigated. Spermine and spermidine were found to be the most efficient polyamines in causing such hydrolysis both in the free DNA and in the nucleosome particles.

Establishment of epithelial cell lines from adult mouse regenerating liver

A simple technique for developing epithelial cell lines from regenerating mouse liver has been described. Twenty-one epithelial cell lines have been developed and can be divided into four groups according to their morphology. All these near diploid cell lines have the capacity to metabolize diverse classes of chemical carcinogens (3-methylcholanthrene, 2-acetylaminofluorene, dimethylnitrosamine and aflatoxin B1) to cytotoxic metabolites. It is not yet possible to determine which ones of these cell lines originated from hepatocytes. Studies are in progress to further characterize and to use these cell lines as lethally irradiated feeder layers for cell-mediated activation of various classes of chemical carcinogens and mutagens with C3H/10T1/2 mouse embryo fibroblasts as indicator cells.

Inhibition of T4 polynucleotide kinase by the ATP analog, beta, gamma-imidoadenylyl 5'-triphosphate

The inhibition of T4 polynucleotide kinase by beta,gamma-imidoadenylyl 5'-triphosphate has been investigated. It was found that the ATP analog was a competitive inhibitor with regard to ATP and a noncompetitive inhibitor with regard to DNA possessing a 5'-hydroxyl group. At pH 8.0, the Ki values were 3 and 11 mM, respectively. beta,gamma-imidoadenylyl 5'-triphosphate was not a substrate in the forward reaction, but would replace ADP and ATP in the reverse reaction. The reverse reaction was also used to make beta,gamma-imidoadenylyl 5'-tetraphosphate.

Physicochemical properties of T4 polynucleotide kinase

Some physicochemical properties of T4 polynucleotide kinase (EC2.7.1.78) have been studied. The enzyme is an oligomer of one polypeptide chain. The molecular weight of the monomer is 33000, as determined from the amino acid analysis. Phenylalanine is the N-terminal amino acid. Each monomer contains two --SH groups, one exposed and one more buried. Circular dichroic spectra suggest a high content of alpha-helical structure, 45--55%. Excitation at 280 nm gave a strong emission fluorescence spectrum with a maximum centering at 340 nm. Sedimentation studies suggested the enzymically active form to be a tetramer. High ionic strength (0.1 M KC1), spermine, and the substrates ATP and thymidine 3'-monophosphate were found to be essential factors in order to stabilize the protein in an oligomeric structure. The association constants for ATP, thymidine 3'-monphosphate, and P1 were determined fluorimetrically to be 7.9 x 105, 4.8 x 105, and 7.2 x 10(2) M-1 respectively.

Phosphorylation of tRNA by T4 polynucleotide kinase

The phosphorylation of various intact tRNA species by T4 polynucleotide kinase has been studied. The apparent Michaelis constant was on the average found to be 100 times lower than for some single-stranded DNAs previously studied. (J.R. Lillehaug and K. Kleppe, (1975) Biochemistry, 14, 1221). Conditions which result in complete phosphorylation of different tRNA species have also been established. Studies on equilibrium constants and the reversibility of the reaction revealed that the phosphorylation reaction is not a true equilibrium reaction under the conditions used in this work.

Phosphorylation of double-stranded DNAs by T4 polynucleotide kinase

The phosphorylation by T4 polynucleotide kinase of various double-stranded DNAs containing defined 5'-hydroxyl end group structures has been studied. Particular emphasis was placed on finding conditions that allow complete phosphorylation. The DNAs employed were homodeoxyoligonucleotides annealed on the corresponding homopolymers, DNA duplexes corresponding to parts of the genes for alanine yeast tRNA, and a suppressor tyrosine tRNA from Escherichia coli. The rate of phosphoylation of DNAs with 5'-hydroxyl groups in gaps was approximately ten times slower than for the corresponding single-stranded DNA. At low concentrations of ATP, 1 muM, incomplete phosphorylation was obtained, whereas with higher concentrations of ATP, 30 muM, complete phosphorylation was achieved. In the case of DNAs with 5'-hydroxyl groups at nicks approximately 30% phosphorylation could be detected using 30 muM ATP. A DNA containing protruding 5'-hydroxyl group ends was phosphorylated to completion using the same conditions as for single-stranded DNA, i.e., a ratio between the concentrations of ATP and 5'-hydroxyl groups of 5:1 and a concentration of ATP of approximately 1 muM. For a number of DNAs containing protruding 3'-hydroxyl group ends and one DNA containing even ends incomplete phosphorylation was found under similar conditions. For all these DNAs a plateau level was observed varying from 20 to 45% of complete phosphorylation. At 20 muM and higher ATP concentrations, the phosphorylation was complete also for these DNAs. With low concentrations of ATP a rapid production of inorganic phosphate was noted for all the latter DNAs. The apparent equilibrium constants for the forward and reverse reaction were determined for a number of different DNAs, and these data revealed that the plateau levels of phosphorylation obtained at low concentrations of ATP for DNAs with protruding 3'-hydroxyl group and even ends is not a true equilibrium resulting from the forward and reverse reaction. It is suggested that the plateau levels are due to formation of inactive enzyme-substrate and enzyme-product complexes. For all double-stranded DNAs tested, except DNAs containing protruding 5'-hydroxyl group ends, addition of KCl to the reaction mixture resulted in a drastic decrease in the rate of phosphorylation, as well as in the maximum level phosphorylated. Spermine, on the other hand, had little influence. Both of these agents have previously been shown to activate T4 polynucleotide kinase using single-stranded DNAs as substrates (Lillehaug, J.R., and Kleppe, K. (1975), Biochemistry 14, 1221). The inhibition of phosphorylation of double-stranded DNAs by salt might be the result of stabilization of the 5'-hydroxyl group regions of these DNAs.

Effect of salts and polyamines on T4 polynucleotide kinase

The activity of T4 polynucleotide kinase (EC 2.7.1.78) was found to be greatly stimulated by salts, such as NaCl and KCl, and polyamines such as spermine and spermidine. Up to a sixfold increase in initial rates was observed with a variety of different single-stranded DNAs and mono- and oligonucleotides. The optimal concentrations of salts were 0.125 M, corresponding to a total ionic strength of mu equals 0.19. For polyamines the optimal concentrations were found to be at approximately 2 mM. With low enzyme concentration and in the absence of activators complete phosphorylation was not achieved for a number of substrates. In the presence of salts or polyamines or high concentration of enzyme the phosphorylation proceeded to completion. Addition of salt led to an increase in both the apparent V-max and the Michaelis constant for the DNA substrate whereas the Michaelis constant of ATP remained unchanged. Polyamines had a similar influence on the kinetic constants for the DNA substrate whereas a decrease was found for the apparent Michaelis constant for ATP. The overall mechanism in the presence of activators was found to be sequential but probably of a rapid equilibrium random type. Of the inorganic anions tested both P-i and PP-i inhibited the enzyme in a competitive manner with both substrates.

Kinetics and specificity of T4 polynucleotide kinase

The kinetics of T4 polynucleotide kinase has been investigated at pH 8.0 and 37 degrees. Double reciprocal plots of initial rates vs. substrate concentrations as well as product inhibition studies have indicated that the enzyme reacts according to the ordered sequential mechanism shown in eq 2 in the text for phosphorylation of a DNA molecule. Based on this mechanism the rate equation for the overall reaction was deduced and the various kinetic constants estimated. Hill plots indicated little or no interaction between active sites in the enzyme. The apparent Michaelis constants and V-max were determined at a fixed ATP concentration, 66 muM, for a number of different substrates varying in chain length, base composition, and nature of the sugar, and a wide variation was found. For the nucleoside 3'-monophosphates tested both the apparent Michaelis constant and V-max values were from approximately 2 to 5 times larger than for the corresponding oligonucleotide. The following orders were obtained with regard to apparent Michaelis constants and V-max for the nucleoside 3'-monophosphates investigated: Michaelis constant, rGP greater than rUp greater than rCp greater than rAp greater than dTp; V-max, rGp greater than rCp greater than rAp greater than dTp greater than rUp. Somewhat similar results were also obtained with the deoxyoligonucleotides tested.

Preparation and separation of d(pT)-10-n oligonucleotides

A series of oligomers having the general formula d(pT)-10-n, n varying from 2 to 20, has been prepared by enzymatic joining of d(pT)-10, annealed on poly dA, employing T-4 polynucleotide ligase. The oligomers could be separated on 8 or 12% polyacrylamide gels. Such oligomers may prove useful as molecular weight markers and initiators for various polymerases.