Mechanical properties, protein-based

The discovery of self-splicing introns showed that RNA could catalyse chemical reactions. Yet, unlike proteins, RNA has no functional groups with pKa values and chemical properties similar to those considered to be important in protein-based enzymes. Steitz and Steitz (1993) postulated that two metal ions were essential for catalysis by ribozymes using a mechanism similar to DNA cleavage, in which a free 3 OH is produced. They proposed,... 

It is often necessary to purify a particular protein to better understand its role in the nutritional value and physicochemical properties of food. Similarly, many enzymes have been purified to study their effect on the texture, color, flavor, and nutritional value of foods. The purification and characterization of protein-based microbial toxins has been necessary to better understand their mechanisms of action and their roles in food-borne disease. 

The mechanical properties of single hydrated dextran microcapsules (< 10 pm in diameter) with an embedded model protein drug have also been measured by the micromanipulation technique, and the information obtained (such as the Young s modulus) was used to derive their average pore size based on a statistical rubber elasticity theory (Ward and Hadley, 1993) and furthermore to predict the protein release rate (Stenekes et al., 2000). 

Although the amino acid sequence as well as the secondary structure of fibroin differs from those of spidroin, the fibers spun from these proteins, that is, silkworm silk and spider silk have comparable mechanical properties. These may be attributed to the structural characteristics, both at the molecular and filament level. The superior mechanical properties of silk-based materials, such as films, coatings, scaffolds, and fibers produced using reconstituted or recombinant silk proteins, are determined by their condensed structures. 

Elastin is typically considered as an amorphous protein consisting of random chain sequences connected by a helical regions. The elastin content varies in elastic fibers such as those found in skin. Elastic fibers are termed oxytalan fibers in the upper dermal layer of skin and they are termed elaunin fibers in the deeper dermis where their elastin content is higher. In vessel wall elastic fibers have recently been differentiated based on histological staining patterns suggesting that differences in mechanical properties of different vessel walls may in part be due to differences in elastin... 

The exclusion of stabilizing solutes from the water adjacent to proteins may also be reduced as temperature is increased, although this effect of temperature on water s properties is not well understood. The preferential exclusion mechanism for protein stabilization, like hydrophobi-cally based stabilization, thus could be temperature dependent and cease to make a strong contribution to protein stability at high temperatures. 

Natural fibers based on cellulose or protein are more prone to degradation due to humidity and temperature than synthetic organic fibers. Photo-degradation occurs when exposed to light (both visible as well as ultraviolet) which shows up as a discoloration and loss in mechanical properties. Most polymeric fibers (natural or synthetic) swell due to moisture absorption. The swelling is generally more in natural fibers. We discuss this topic again in Chapter 4. 

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