ALKYLATING AGENTS AND NUCLEIC ACIDS 503 only if alkylation on each strand at nearly opposite points had occurred. At low degrees of alkylation by monofunctional agents this would occur only rarely, being in proportion to the square of the degree of alkylation; with difunctional agents about a quarter of the alkylations would be of this type. It would also be expected that fission of the DNA molecule could seriously interfere with its biological function. SUMMARY 1. The rates and extents of alkylation of ribonucleic acid and of deoxyribonucleic acid in neutral aqueous solution at 370 by a variety of alkylating agents have been determined. 2. Alkylation has been shown to occur at N-7 of guanine moieties, monofunctional agents yielding 7-alkylguanines, and difunctional agents yielding in addition di(guanin-7-yl) derivatives. 3. Alkylated ribonucleic acid is stable in neutral aqueous solution but alkylated deoxyribonucleic acid decomposes with loss of the alkylated guanine products. 4. The extent of binding has been determined of 3H-labelled myleran, 35S-labelled mustard gas and of 2-hydroxyethyl 2-chloroethyl [35S]sulphide to cellular constituents of the Ehrlich-ascites tumour and of 3H-labelled myleran to leukaemic cells in the mouse. 5. The only difference found in vivo or in vitro for reaction of mustard gas and 2-hydroxyethyl 2-chloroethyl sulphide with nucleic acids is that mustard gas yields di-(P-guanin-7-yl) sulphide. 6. Mustard gas is at least 30 times as effective as 2-hydroxyethyl 2-chloroethyl sulphide as an inhibitor of the growth of an ascites tumour in the mouse. 7. The mode of combination of monofunctional and of difunctional alkylating agents with nucleic acids is discussed in terms of the Crick-Watson model for the structure of deoxyribonucleic acid. 8. The possible relationship between the alkyl-ation of deoxyribonucleic acid and the biological properties of the alkylating agents is discussed. We thank Dr J. F. A.
An aqueous 1% solution of sodium dodecyl sulphate (SDS) will completely dissolve the myofibrillar proteins of fresh cod flesh, and of cod flesh stored at –14° until it is very tough. With the aim of detecting the formation of detergent stable intermolecular protein crosslinks during cold storage of cod flesh, a comparison has been made of the weight and z‐average molecular weights of the mixture of components in detergent solutions prepared from fresh cod flesh and cod flesh stored at –14° for various periods of time. This comparison has shown that very few, if any, such crosslinks are formed during cold storage of the flesh. By separately determining the average molecular weights of the individual constituent myofibrillar proteins in detergent solutions, probable limits to the extent of intermolecular crosslinking in the cold stored flesh by detergent‐stable bonds could be established.
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