Sarcoplasmic membrane composition

H and N NMR techniques were used to investigate the membrane composition, orientation, and side-chain dynamics of the transmembrane segment of phospholamban, a sarcoplasmic Ca " -regulator protein. ... 

The protein components of a membrane can be readily visualized by SDS-polyacrylamide gel electrophoresis. As discussed earlier (Section 4.1.4). the electrophoretic mobility of many proteins in SDS-containing gels depends on the mass rather than on the net charge of the protein. The gel-electrophoresis patterns of three membranes—the plasma membrane of erythrocytes, the photoreceptor membrane of retinal rod cells, and the sarcoplasmic reticulum membrane of muscle—are shown in Figure 12.16. It is evident that each of these three membranes contains many proteins but has a distinct protein composition. In general, membranes performing different functions contain different repertoires of proteins. 

A very attractive candidate for structural studies on biological membrane are vesicles of sarcoplasmic reticulum from striated muscle. It is characterized by a high degree of homogeneity, both from the compositional and from the functional point of view more than 90% of the total protein is constituted by the Ca " -... 

What studies have been performed One of the more interesting of the few studies that exist was the examination of the activity of the Ca2+ adenosinetriphosphatase (ATPase) of sarcoplasmic reticulum membranes that were reconstituted into bilayer vesicles of different, defined lipid compositions (38). This survey found that the activity, which may be defined as the number of Ca2+ pumped across the bilayer per adenosine 5 -triphosphate (ATP) hydrolyzed, correlated strongly with the Hu tendencies of the imbedding lipid bilayer. For example, activities were high in compositions rich in either DOPE or MGDG, both of which readily form low-temperature Hu phases. By contrast, activities were low in DOPC or DGDG, as well as in other lipids that do not readily form Hu phases. Decreasing the amount of... 

Factors that affect texture include moisture content, composition, variety or species, pH, product history (maturation or age), and sample dimensions. Texture is also dependeut on the method of dehydration and pretreatments. Purslow [55] stated that meat texture is affected by the structure of the solid matrix. He coucluded that it is important to have a fundamental understanding of the fracture behavior of meat and how it relates to the structure of the material. Stanley [83] stated that many researchers now believe that the major structural factors affecting meat texture are associated with connective tissues aud myofibrillar proteins. Moreover, two other components muscle membranes and water also deserve consideration not because of their inherent physical properties, but rather as a result of the indirect influence they have on the physical properties. It should be noted that sarcoplasmic proteins may be important for the same reason, although little information on their role is available. He suggested that these structures merit particular attention. 

THE LIPID COMPOSITION AND Ca TRANSPORT FUNCTION OF SARCOPLASMIC RETICULUM(SR) MEMBRANES DURING DEVELOPMENT IN VIVO AND IN VITRO... 

Other fatty acids varied to a lesser extent. The accumulation of unsaturated fatty acids occurs with an increase in chain length which would mantain the fluidity of the membrane constant, suggesting that these variations in fatty acid composition do not contribute significantly to the observed changes in Ca transport during muscle development in vivo. This is supported by the lack of changes in passive Ca permeability observed in sarcoplasmic reticulum membranes isolated from developing embryos and chicks (Martonosi, 1975). 

During development of chicken skeletal muscle cells, the marked increase in Ca transport of sarcoplasmic reticulum, observed both in vivo and in vitro systems, can be interpreted mainly as the result of an increase in the concentration of Ca transport ATPase. Changes in the fatty acid composition of muscle membranes developed in vivo occur with a balance between chain length and unsaturation, without affecting significantly their Ca permeability. In cultured muscle cells their fatty acid composition can be manipulated to a great extent by lipid supplementation of the culture medium. The effects of these in vitro modifications in lipid composition on the calcium transport function of muscle membranes should be investigated. 

---