462 NATURE September 15, 1951 voL. 16a may also be unhydrolysed nucleotide. Extraction of correct asswnption that the prosthetic group is the spots and identification by ultra-violet absorption adenosine triphosphate instead of the dinucleotide. measurements has not been successful, since the G-actin contains the dinucleotide which is rich in amyl alcohol used in the chromatography is con­ phosphorus, and F-actin contains the dinucleotide taminated by a substance with absorption in this poorer in phosphorus. During the transformation of region. Purification of the amyl alcohol has been G-actin into F-actin, the phosphorus-rich and there­ unsuccessful, and it has not yet been possible to get fore more labile dinucleotide gives off one phosphoric a synthesized amyl alcohol. acid residue and is transformed into the dinucleotide These investigations show that the prosthetic group of F-actin. is a dinucleotide. Kornberg3 has &hown that diphos­ Upon contraction in vitro of actomyosin with phopyridine nucleotide (co-zymase, co-enzyme I) can adenosine triphosphate, the myosin splits off a undergo a direct phosphorylation to triphospho­ phosphoric acid residue of the triphosphate. It is pyridine nucleotide ( co-enzyme II) by adenosine possible for the energy-poor dinucleotide in F-actin triphosphate and a yeast enzyme. Since the di­ to take up such a phosphoric acid residue in the nucleotide described here has the same characteristic, nascent state. F-actin is thus transformed to G-actin one may suppose an analogous &tructure. However, during the contraction. it does not seem to contain nicotinic amide but Straub et al. have found that when F-actin is another as yet unidentified substance with basic dialysed against a solution of adenosine triphosphate properties. for a longer time, the F-actin is converted into Further investigations are going on, and a more G-actin. At the same time adenosine triphosphate detailed description will appear elsewhere. disappears and adenosine diphosphate appears. He The investigation is being supported financially by assumes that the diphm,phate in F-actin takes the the Swedish Natural Science Research Council. place of triphosphate. From our results the process BERTIL GEL0TTE is better explained by assuming that the dinucleotide residue from the adenosine 1 GeJotte, B., Biochim. Biophys. Acta (in the press). takes up a phosphoric acid ' Snellman, 0., and Gclotte, Il. (see preceding communications). triphosphate QI1 account of its instability ; it always "Kornberg, A., J. Biol. Chem., 182, 805 (19"(,). loses phosphorus gradually with time. We have also found that the dinucleotide can take up phosphoric acid residues given off by the adenosine triphosphate The Prosthetic Group of Actin in such a manner. It seems thus that adenosine triphosphate does not A STUDY of the prosthetic group of G-actin and play the dominant part previously assigned to it in F'-actin has been made with paper chromatography, the contraction process. This role may be taken by a using as solvent an aqueous solution of 5 per cent dinucleotide ( one group of which is adenosine, the dibasic sodium phosphate and a solution of 0·5 per other is not yet identified) which can take up and cent lauryl amine in amyl alcohol as described else­ give off a phosphoric acid residue. The adenosine ,.-here1. We could detect only one spot when investi­ triphosphate acts as a phosphorus donor. gating the prosthetic group of F-actin, the RF value In many respects this dinucleotide resembles of which was 0·67. From G-actin also only one spot cozymase, which also occurs both as a phosphorus­ was visible, with the RF value 0·64. These RF values rich and a phosphorus-poor compound (co-enzyme II correspond to the values found for the phosphate­ and I). A comparison of the dinucleotide with absorbing protein derived from the actomyosin cozymase has shown that they are not identical. complex reported in another communication•. Acid Further details of these investigations, which were hydrolysis of the prosthetic groups from the two supported financially by the Swedish Natura,! Science kinds of actin showed, upon paper chromatography, Research Council, will be given elsewhere. identical spots with the RF values 0·40 and 0·85 OLLE SNELLMAN respectively. The prosthetic group of actin is a BERTIL GEL0TTE dinucleotide containing adenosine and another hither­ Institute of Biochemistry, to unidentified base. This dinucleotide can occur in Uppsala. two forms, one richer in phosphorus (in G-actin) ahd April 25. the other poorer in phosphorus (in F-actin). It may 1 S.1clhna.n, 0 ., and -Oelotte, B. (see preceding communication). be mentioned that in no circumstances have any • Oelotte, B. (see preceding communication). spots derived from adenosine tri- or di-phosphate been 'Straub, F. n., "nd Feuer, 0., Biochim. Biophys, Acta, 4, 455 (1950). detected. The RF values for these substances under the same conditions are 0·83 and 0·76, so they must occur in insignificant amounts. CHEMISTRY OF CANCER Earlier, Straub et al. 3 have found that actin contains a prosthetic group which they consider to be adenosine MEETING, under the joint auspices of the triphosphate in G-actin, and which during the poly­ A Chemical Society, the Royal Institute of merization of G-actin to F-actin splits off one phos­ Chemistry, the Society of Chemical Industry, and phoric acid residue and is transformed into adenosine the Institute of Petroleum, was held in Manchester diphosphate. on March 15, with the general title "The Chemistry 'I'he absorption spectrwn of the isolated prosthetic of Cell Division". The proceedings were sadly inter­ group in a Beckman spectrophotometer gives a curve rupted by the sudden death of Prof. G. A. R. Kon which resembles that of an adenosine derivative. while contributing to the discussion at the end of The relation of the absorption curve to pH, however, the morning session, and the meeting was abandoned. is different from that of an adenosine phosphoric Three papers were, however, read. acid. It seems also that the prosthetic group can in In his introductory survey, Prof. A. Haddow dealt certain circwnstances be split, giving off adenosine- with the biological effects (tumour-inhibitory, cyto­ 5-phosphate, which can be deaminated by Schmidt's logical and carcinogenic) of cytotoxic substances, with <leaminase. These results have supported the in- special reference to the nitrogen mustards. It is © 1951 Nature Publishing Group.