The relative stabilities of the skeletal-muscle myosins of some animals

Abstract

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.

The Conformational Stabilities of Tropomyosins

“…There are several reported instances of a correlation between the stability of proteins (usually taken as the temperature at which the molecule is half unfolded) and the preferred temperature range at which species exist. These include the thermal transitions of collagen (Rigby and Robinson 1975), the denaturation of skeletal muscle myosins by heat and urea (Connell 1961), and the thermostability of fish myofibrillar ATPases (Johnston et al 1973). However, more data would be required to test this hypothesis for tropomyosins.…”

Antioxidative Ability of Chicken Myofibrillar Protein Developed by Glycosylation and Changes in the Solubility and Thermal Stability

“…Takeda et al have examined the feasibility of industrial application and indicated the strong potential of protein glycosylation for use with spawned-out chum salmon. 15) Fish muscular protein is thermally less stable than that of other vertebrates, 16) and a comparatively large amount of sugar has to be used in the glycosylation process to prevent the denaturation of fish meat protein. 17) Saeki and Inoue have used as much as 9-fold the amount of glucose to protein weight to make the myofibrillar protein of carp soluble in a low ionic strength medium by glycosylation.…”

The Characterisation of the 5′ Regulatory Region of a Temperature‐Induced Myosin‐Heavy‐Chain Gene Associated with Myotomal Muscle Growth in the Carp

“…Isolated myofibril studies showed that carp adapted to low temperatures (8 "C) developed a higher specific ATPase activity whilst the converse was true for those adapted to a warm temperature (25°C). This is accompanied by changes in the thermostability of the myofibrillar system with the cold-adapted fish myofibrils becoming more susceptible to thermal denaturation (Connell, 1960(Connell, , 1961. Measurements on isolated fibre bundles (Langfeld et al, 1991) have shown that forcehelocity characteristics of the muscle are higher in cold-adapted fish when measurements are performed at a low temperature, improving the contractile performance of slow muscle fibres.…”