1952
J. W. RICHTER,D. E. AYER,A. W, BAZEMORE, X. G. BRINKAND KARLFOLKERS Vol. 7 3 [CONTRIBUTION FROM THE
Pituitary Hormones.
RESEARCH LABDRATORIES O F MERCK& CO.,INC.]
V. The Purification of Corticotropin-B by Ion-exchange Techniques
BY JOHN W. RICHTER,DONALD E. AYER, ALVAW. BAZEMORE, NORMAN G. BRINKAND KARLFOLKERS RECEIVED SEPTEMBER 8, 1932 Methods have been developed for the purification of concentrates of corticotropin-B by ion-exchange techniques. Corticotropin-B undergoes exchange on columns of the cation-exchange resin Amberlite IRC-50 buffered with sodium ions, while inert materials are eluted by washing with aqueous pyridine and aqueous acetic acid solutions. The active principle is the11 removed from the resin by dilute hydrochloric acid, and is recovered as a solid hydrochloride, which is free of inorganic salts, and which possesses an activity of 250 t o 300 u./mg. Considerable purification is also obtained by fractionation on columns of oxycellulose. In these processes, the presence of a reducing agent such as sulfite or hydrogen sulfide has inhibited inactivation and has made possible better separations and more highly active products.
At the time that work on the ACTH problem was initiated in this Laboratory, it was considered that the active principle of the pepsin digests of the “ACTH protein”1~2 might be a small peptide with a chain of six to eight amino acid units.3 It seemed likely that such a molecule should be amenable to purification by ion-exchange techniques and, accordingly, studies to this end were begun. I t now appears that corticotropin-B, a very potent active principle of pepsin-digested corticotropin, is of considerably higher molecular weight. White, Fierce and Lesh have recently suggested4 that pzrtially pepsin digested material behaved more like a protein than a small peptide during paper chromztography. A molecular weight in the ranqe of 5,000 to 6,000 has been advanced on the basis of ultracentrifugal studies and the amino acid compoposition of highly purified corticotropin-B .5 Despite this higher molecular weight, purification of corticotropin-B has been achieved by ion-exchange techniques by us and other workers. The excellent process for the purification of crude extracts of corticotropin to the 80-u./1ng. level with oxycellulose probably operates by an ionexchange mechanism.6 Elsewhere, crude corticotropin and ACTH “protein hormone’’ were chrom-itographed on the cation-exchange resin Amberlite IRC-50, using- a $H 6.8 phosphate buffer.’ The adrenocorticotropic activity was separated in this way from the bulk of the proteinaceous materials, and was indicated by its behavior to be a basic substance. Althougli proteinaceous molecules are usually too large to undergo ion-exchange with ordinary resins, in isolated instances compounds of relatively high molecular weight have been successfully fractionated by chromatography on Amberlite IRC-50, as has been shown by the recently reported purifications of t h e basic proteins ribonuclease,8 lysozymes and cytochrome-cgby this method. (1) C. H. Li, II. hl. Evans a n d M. E. S i m p s o n , J . Biol. Chern., 1 4 9 , 413 (1943). (2) G. Sayers, A. White and C . X, H. Long. i b i d . , 149, 125 (19431. (3) C. H.Li,Trans. Conf. o n Metabolic Aspects of Convalescence, Josiah Macy, Jr., Foundation, New York, N. Y., 1948, p. 11L (4) W. F. White, W. L. Fierce and J. B. Lesh, Proc. Soc. E n p f l . Biol. Med., 78, 616 (1951). (5) N. G. Brink, G. E. Boxer, V. C. Jelinek, F. -4.Ruehl, Jr., J. W. Richter and K. Folkers, Tars J O U R N A L , 76, 1980 (1953). (6) E. B. Aatwood, M. S. Raben, R. W. Payne and A. B. Grady, ibid., 1 8 , 2969 (1951). (7) H. B. F. Dixon, S. Moore, hl. P. Stack-Dunne and F. C.Young, h‘afure, 168, 1044 (1951). (8) C. H.W. Hirs, W. 11. Stein and S. Moore, T r r s J O U K s a I . , 73, 1893 (1951). (9) S. Paleus and J. B. Nielands, Acfa Ciicrn. Scond., 4 , 1024 (1930).
Early in our study of the use of ion-exchange resins, it was noted that the highly active principle of corticotropin-B concentrates underwent exchange almost quantitatively with the cation-exchanger Amberlite IRC-50 butfered with sodium ions; that it was tightly held on the resin, indicating a strongly basic character; and that it could be eluted with hydrochloric acid. It also soon became evident that troublesome inactivations, apparently oxidative in n a t ~ r e ,could ~ , ~ be prevented or minimized by the presence’of reducing agents. Sodium sulfite was used in neutral or weakly alkaline solutions, and hydrogen sulfide was added to acidic solutions. This precaution resulted in sharper separations during the ion-exchange fractionations, and gave products of higher activity than were obtained without the use of the reducing agents. These observations led to procedures which gave some threefold enhancement of the activity of corticotropin-B concentrates beyond the 60- to 100-u./ mg. level. The active material of such concentrates’O was allowed to undergo exchange with a sodium-buffered column of Amberlite IRC-50. A substantial amount of inactive proteinaceous material was removed from the column by washing it with aqueous pyridine; and other proteins, pyridine and sodium ions were eluted with aqueous acetic acid. An active concentrate (a. 150 u./ mg.) was eluted by washing the column with 0.01 N hydrochloric acid solution (PH2.0). Finally, the remainder of the corticotropin-B was removed from the column by elution with hydrochloric acid solution of PH 1.6 and ms recovered as a white, amorphous solid with an activity of approximately 250 to 300 u./mg. When the process designated procedure A in Table I was used, hydrogen sulfide was present in all of the solutions employed during the resin purification. Procedure B differed only in that sodiurn sulfite was substituted for hydrogen sulfide in the steps prior to elution of the column with acid. The results from a number of such purifications are summsrized in Table I. The results indicated above and those described in detail in the Experimental section represent typical good experiments. At times, the results were less satisfactory, with lower yields and products of lower activity. One factor which has on occasion affected the success of the process has been contamination of the starting I I I iterials with heavy metals. Such samples showed 10) \ T I ‘ Rnzcmore. J W Richter, D. E A y e r , J Finnerty, N G Brink and K I olkers THIS J O U K V ~ L ,76, 1949 (1953)
April 20, 1953
PURIFICATION OF CORTICOTROPIN-B BY ION-EXCHANGE
dark precipitates in the presence of hydrogen sulfide, and the products from these preparations tended to be low in activity. Another cause of occasional difficulty may have been the presence in samples of starting material of inactivation products so closely resembling corticotropin-B in properties as to make separation difficult. I t must be strongly emphasized that due to variations and uncertainties in the bioassay, the values for activities and yields are to be regarded as approximate, even though replicate assays were obtained on some samples. Despite these difficulties, this type of purification procedure has been easy to carry out and adaptable to the handling of large quantities of material. The highly active products were readily recovered in stable form as the dry, solid hydrochloride, free of inorganic contaminants. ~'URIFICATION OF
TABLEI CORTICOTROPIN-B CONCENTRATES ON AMBERLITE IRC-50
S t a c i n g material Proce. G. u./mg. dure
280 mg. ,300 mg.
80 80
A" A"
1.6
90
Ab
1.0
80
Bb
2.0
60
Ab
1.3 1.0 300 mg.' 2.6' 1.2 1 .o 1.9 1.7 2.0 1.5
76 50 80 75 75 50 60 75 40 40
Ab Ab Ab AC Ab Bb Bb Bb Bb Bb
Mg.
45 300d 60 300(?) 40 300d 198 200 306 350d 100 150 40 375d 50 275 190 240 140 300 225 250 210 150 Low activity 450 150 Low activity 130 300 235 260 375 275 310 140 210 220 nnn
LUU
1.45
55
Bb
Product u./mg.
80 500
3c)n
LJU
200 130
Recovery of activity, %
60 75( ?) 50 27 75 20 19 17 38 35 58 63 (?)
35
