Incorporation of Canavanine Into Protein of Vvalker Carcinosarcoma 256 Cells Cultured in Vitro
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Incorporation of Canavanine into Protein of VValker Carcinosarcoma 256 Cells Cultured in Vitro PAUL F. KRUSE, JR., PAT B. WHITE, HENRY A. CARTER, AND THOMAS A. McCoY (Biomedical Ds~ision, The Samuel Roberts Noble Foundation, Inc., Ardraore, Okla.) The inhibitory effect of canavanine on the exposure to the arginine-deficient medium for 4~) growth of Walker carcinosarcoma ~56 cells in minutes, sufficient L-canavanine .H2SO41 (~0.9 vitro was described in a previous report (9). Ap- mg. dissolved in Earle's balanced salt solution) parently, the inhibition rested in a competitive was added to produce a final concentration of 0.~0 interference of canavanine with the utilization of mM (10:1 ratio of canavanine to arginine). The arginine. inhibited cultures were incubated for ~4 hours and A number of recent reports have demonstrated allowed to stand at 4 ~ C. for ~ hours to free the that certain amino acid analogs--e.g., ethionine cells from the glass (1~); cell counts indicated a (6, 10, ~, ~6), p-fluorophenylalanine (2, 17, 9.~5), total of 104 X 106 cells. The contents of the flasks fl-~-thienylalanine (17), selenomethionine (4), 7- were combined and centrifuged in ~50-ml. bottles azatryptophan (18, 19), and tryptazan (3)--can for 6 minutes at 2750Xg. The cell buttons were be utilized in place of their respective metabolic transferred ~u a 15-ml. centrifuge tube and counterparts for protein synthesis. Accordingly, washed 3 times with 5-10-ml. portions of Earle's it was of interest to determine whether the tumor solution minus CaCl~. The cells were then ex- cells could utilize canavanine in this manner as a tracted successively with 80 per cent ethanol, substitute for arginine. If so, a contributing factor ethanol-ether (1:1), and cold 10 per cent tri- in the inhibition of growth could have been a sub- chloroacetic acid (TCA). The residue was sus- sequent malfunction of the resultant protein. pended in s ml. of 5 per cent TCA, heated for 15 Canavanine has not been shown to participate in minutes in an oil bath at 90 ~ C., allowed to cool, protein synthesis and has been reported (7) to and washed twice with water. It was next heated exist only in the free state in the Jack bean, its for 15 minutes in s ml. of 0.1 ~r NaOH in an oil principal source. bath at 60 ~ C., reprecipitated with 2 ml. of s per In the present investigation it was interesting, cent TCA, and washed with water. Next, the therefore, to find an appreciable incorporation of residue was washed with absolute ethanol, etha- canavanine in the tumor cell protein. nol-ether (1:~), ether, dried in vacuo for 7 hours (37.1 rag.), and hydrolyzed by being refluxed in MATERIALS AND METHODS 3.0 ml. of 6 N HC1 for 18 hours. The hydrolysate Tissue cultures.--Suspensions of freshly excised was taken to dryness twice in vacuo, and the Walker tumor cells were cultured in T-60 flasks. residue was dissolved in pH 3.1 citrate buffer (14) All operations were performed aseptically, solu- and clarified by centrifugation. Eighty per cent of tions were sterilized by passage through Selas the solution was chromatographed. filters, and growth was determined by cell counts. A "control" protein hydrolysate was obtained An initial inoculum of ~00,000 cells/ml was used, as follows: After 48 hours' incubation, cell counts and the cells were established in medium, 20 ml/ indicated a total of 157 X 106 cells in 16 T-60 flask culture, containing fourteen essential amino acids, cultures (minus canavanine). Two milliliters of a serine, glycine, vitamins, antibiotics, salts, glucose, solution of L-canavanine .H2SO4 in Earle's solu- and dialyzed human serum (11). tion, 1 mg/ml, were added to each culture. After Incorporation of canavanine.--After incubation standing at room temperature for 15 minutes, the at 87~ C. for $4 hours, the medium was withdrawn cells were separated from the medium and washed from nineteen T-60 flask cultures and replaced as described above. The cell button was suspended with an identical medium, except that the arginine in 1 ml. of the canavanine-Earle's solution, and content was reduced from 0.s to 0.0~ inM. After 1Purchased from California Foundation for Biochemical Received for publication August 28, 1958. Research. 12~ Downloaded from cancerres.aacrjournals.org on October 2, 2021. © 1959 American Association for Cancer Research. :KRUSE et al.--Canavanine Incorporation in Walker 256 Protein 1~3 6.7 ml. of 90 per cent ethanol was added. After The calculations were made from a standard thorough mixing, the cell residue was centrifuged curve of ninhydrin analysis of L-leucine;2 the color and treated with the series of extractions outlined yield of canavanine relative to leucine was found above. The amounts of extractants were increased to be 1.01. The quantities of histidine, canavanine, in proportion to the number of cells. The protein and arginine were corrected for the recoveries-- residue, 45.7 rag., was hydrolyzed by being re- 91.0, 82.5, and 98.8 per cent, respectively--which fluxed in 8.7 ml. of 6 N HC1 and treated as above. were obtained from chromatography of the "hy- Seventy per cent of the hydrolysate was chro- drolyzed" mixture of nineteen amino acids) matographed. The chromatographic conditions caused lysine Chromatography of canavine and protein hydroly- and ammonia to emerge together in the eluate, sates.--Ion exchange chromatography was per- permitting canavanine to emerge shortly there- formed as described by Moore and Stein (12, after as an isolated substance. Two coincident 13), with a 1.2 X 20-cm. column of 200-mesh 80-20 mixture of Dowex 50-x4,-x5. The column P.o was operated at room temperature, at a flow rate of 9-10 ml/hr, and 0.95 (control) and 0.91 1.5 i A (canavanine) ml. fractions were collected. Prior I.o to chromatography of the protein hydrolysates, a mixture of nineteen amino acids (including canavanine), which had been subjected to hydroly- >- sis conditions, was chromatographed. Location and o~-o.2t- quantities of amino acids in the effluent were determined by ninhydrin analysis (15); alternate t~ _j 0 ~L2:::2:2:~ fractions in the region of canavanine elution were <~.o also analyzed by the colorimetric procedure of ~_o Archibald (1). a. Z 0 1.5 0 RESULTS 3E In preliminary experiments with 1 : 1 and 2:1 1.0 4" w z exogenous canavanine-arginine ratios and 20-48 • z < r.~ 106 cells, the antimetabolite was not readily de- 0.5 tectable in the protein hydrolysates. It appeared likely, however, that interference with arginine i 0 --= incorporation had occurred, since the molar ar- I00 150 200 25O ginine/histidine ratio was always uniformly lower FRACTION NUMBER than that in protein from uninhibited cells. When CHART 1.--Chromatography of protein hydrolysates from the number of cells and the canavanine concen- Walker carcinosarcoma 256 cells cultured without (A) and tration were increased approximately two- and with (B) eanavanine. For culture and chromatographic condi- tenfold, respectively, and the cells were treated tions, see text. for a short time in arginine-deficient medium prior to introduction of the antimetabolite, canav- color peaks were obtained when alternate fractions anine was readily detectable in the protein hy- in the canavanine region of the eluate were ana- drolysate, as illustrated in Chart 1. Here the lyzed with ninhydrin (14) and alkaline nitroprus- histidine, canavanine, and arginine peaks were cal- side (1). None of the fractions in adjacent regions culated to represent 6.11, 1.60, and 13.42 gmoles, gave the nitroprusside test. respectively, in the total protein hydrolysate; in DISCUSSION the control hydrolysate (from Chart 1), the quan- tities of histidine and arginine were 7.82 and The most likely explanation of the above results 19.18 /zmoles in the total hydrolysate. Thus in is that canavanine participated in protein syn- the presence of canavanine the arginine/histidine thesis and became a part of the polypeptide chain. ratio was 2.20 in contrast to 2.45 for the con- The possibility that canavanine was merely ab- trol. However, the combined canavanine-arginine/ Purchased from H and M Chemical Co., AP grade. histidine ratio, 2.46, matched that of the con- s The assumption that these recoveries would be the same trol. The ratio of the amount of antimetabolite/ for amino acids released from peptide linkage during hy- drolysis may not be valid, but the figures do agree with the metabolite in the protein under these conditions report (8) that canavanine is more labile to acid hydrolysis was 0.12. conditions than is arginine. Downloaded from cancerres.aacrjournals.org on October 2, 2021. © 1959 American Association for Cancer Research. 1~4 Cancer Research Vol. 19, January, 1959 sorbed on the precipitated, amorphous protein nine permitted an approximate doubling of the pro- was virtually eliminated in the control experi- tein of a strain of E. coli, whereas canavanine ment. Additional evidence of incorporation was was incapable of substituting for arginine in that seen in the change in arginine content, as meas- respect. The degree of incorporation into protein ured by its relationship to histidine. In the pres- of the two analogs was not measured. Recently, ence of canavanine the ratio of these two amino Yoshida (26) found that one third of the methio- acids was always lowered. The combined arginine- nine in a-amylase produced during culture of B. canavanine content, however, was of the same 8ubtilis could be replaced with ethionine. Whether order of magnitude with respect to histidine as the different degrees of incorporation of analogs arginine alone in the protein of uninhibited cells.