Light-scattering Raleigh linewidth measurements on G-actin

Abstract

chloride). The rate and extent of superprecipitation of natural actomyosin fronm white fibres were 25-50% greater than those of natural actomyosin from red fibres. It remains to be established how the contraction times of the red fibres and the white fibres are related to their myosin adenosine triphosphatase activities.Briskey, E. J., Sayre, R. N. & Cassens, R. G. (1962). J.Fd Sci. 27, 6. Dubowitz, V. (1970) Muscle becomes hard and inextensible during the onset of rigor (Bendall, 1960), but during subsequent storage at 2°C there is a progressive increase in tenderness. The ability to maintain isometric tension is lost (Jungk, Snyder, Goll & McConnell, 1967), but the muscle does not regain its extensibility. These changes during storage are believed to be caused by post-mortem autolysis. A study of the myofibrillar ultrastructural changes over the storage period essential to an understanding of the nature of this autolysis is reported. Proteolysis in the sarcoplasmic fraction and release of lysosomal cathepsin D were also investigated.Bovine semitendinosus muscle was sampled immediately post mortem and after 24h, 4 days and 10 days storage at 20C for light and electron microscopy. The supernatants obtained after centrifuging homogenates from Oh, 2-day and 15-day post-mortem samples for 30min at lOOOg (ra,. 7.62 cm) at 40C were applied to an exponential sucrose density gradient in the BXIV aluminium zonal rotor and centrifuged for 45min at 43000g (ray. 4.7cm) at 50C. Collected fractions were analysed for protein (Schuel & Schuel, 1967) and cathepsin D activity ((Anson, 1937).The phase-contrast microscope showed a progressive increase in incidence of transverse fibre breaks during the storage period. These breaks always occurred in the I band.Pre-rigor myofibrils in the electron microscope had the appearance of resting muscle (Huxley, 1960). The Z lines showed a well-defined fibrillar pattern (Landon, 1970), which gradually turned amorphous during subsequent storage. The other components of the myofibril were not significantly affected by storage for 10 days. The ultrastructural locus of the fibre breaks seen in the light microscope was the Z line/I band junction (Revile, Joseph & Harrington, 1971).The amount of sedimentable protein decreased during storage. In pre-rigor samples 52.5% of the total protein was sedimentable, whereas 2-day samples showed 27.5% and 15-day samples only 18% sedimentable protein.The total activity of cathepsin D did not change appreciably over the storage period, but of this 84.5% was sedimentable in pre-rigor samples and 40.7 % after 15 days.The limited and specific ultrastructural disruption of the myofibrillar fraction occurring during storage would undoubtedly result in increased tenderness and loss of ability to mnaintain isometric tension. The sarcoplasmic fraction undergoes a more extensive autolysis, but all the cathepsin D activity does not seem to be released during storage. This agrees with Valin (1970). Anson, M. L. (1937). J. gen. Physiol. 20, 565. Bendall, J. R. (1960 Lig...

Strategizing Human Development for a Country in Transition from a Resource-Based to a Knowledge-Based Economy

“…There should be developed life-long learning, job training, and skills improvement strategies linked to industrial demand to implement and efficiently use Policy 1 [102]. Furthermore, the industrial sector must be involved as a co-designer in the curriculum [103]. It is also important to consider teachers, who are the main party involved in Policy 1.…”

Collagenases and Elastases

“…According to Graham (134) the inhibitor is associated with the a2 globulin fraction. It is very similar to (134,135), but not identical with (12), serum trypsin inhibitor or plasma inhibitor. It is very similar to (134,135), but not identical with (12), serum trypsin inhibitor or plasma inhibitor.…”

“…Walford and Schneider (443) think that it resides in the a1 globulin/albumin fraction of serum, but is not simply proport(iona1 to the level of either, though the highest and lowest inhibitor concentrations were found in sera with the highest and lowest a1 globulin content, respectively. Its action could be completely reversed by adding a stoichiometric amount of trypsin, analogous to the release of active elastase from proelastase by trypsin (134,135,138). Its action could be completely reversed by adding a stoichiometric amount of trypsin, analogous to the release of active elastase from proelastase by trypsin (134,135,138).…”