Fibrous hydrolysis

Solution Process. With the exception of fibrous triacetate, practically all cellulose acetate is manufactured by a solution process using sulfuric acid catalyst with acetic anhydride in an acetic acid solvent. An excellent description of this process is given (85). In the process (Fig. 8), cellulose (ca 400 kg) is treated with ca 1200 kg acetic anhydride in 1600 kg acetic acid solvent and 28—40 kg sulfuric acid (7—10% based on cellulose) as catalyst. During the exothermic reaction, the temperature is controlled at 40—45°C to minimize cellulose degradation. After the reaction solution becomes clear and fiber-free and the desired viscosity has been achieved, sufficient aqueous acetic acid (60—70% acid) is added to destroy the excess anhydride and provide 10—15% free water for hydrolysis. At this point, the sulfuric acid catalyst may be partially neutralized with calcium, magnesium, or sodium salts for better control of product molecular weight. 

Yoshioka et al. investigated the catalytic activity of polystyrene-polypropylene fibrous cation-exchange resins in the hydrolysis of sucrose [26]. Owing to their higher surface area than that of traditional cation-exchange resins, the accessibility of the catalytic sites to sucrose was greatly improved. Therefore, polystyrene-polypropylene-based cation-exchange resin was more active than conventionally used... 

Figure 19-18 Simplified view of the ATP hydrolysis cycle for actomyosin. A similar cycle can be written for kinesins and dyneins. Here A stands for fibrous actin and M, M, M, and M for four different conformations of the myosin heads.

Metabolism of pectin. Pectin has only recently come, to be considered a part of the dietary fiber complex. Previously it was excluded because 1) it is not fibrous (except at the molecular level), 2) it escapes detection in standard fiber tests owing to its solubility, and 3) it usually does not survive intestinal passage. In a reassessment of which dietary components should be considered fiber, Trowell (49) proposed that dietary fiber include those constituents of food resistant to hydrolysis by man s alimentary enzymes. Spiller (50, 51) suggested that confusion surrounding the term "fiber" be avoided by using the term "plantix" to denote those plant materials of polymeric nature not attacked by human digestive enzymes. 

Actin, the major constituent of the thin filaments, exists in two forms. In solutions of low ionic strength it exists as a 42kDa monomer, termed G-actin because of its globular shape. As the ionic strength of the solution rises to that at the physiological level, G-actin polymerizes into a fibrous form, F-actin, that resembles the thin filaments found in muscle. Although actin, like myosin, is an ATPase, the hydrolysis of ATP is not involved in the contraction-relaxation cycle of muscle but rather in the assembly and disassembly of the actin filament. 

According to Ro et al.17 gels made from low water content sols contain residual organic groups, caused by incomplete hydrolysis, which contributes to the formation of micropores during the thermal treatment. Acid-catalyzed gels show slit-shaped micropores and have a fibrous or plate-like structure. Base-catalyzed gels have cylindrical pores and spherical particles. 

These serine proteases are used to remove pathogens by their hydrolytic activity. They degrade cell membrane proteins and connective tissue matrices by hydrolysis of extracellular matrix proteins such as fibronectin, type IV collagen and laminin, or solubilizing fibrous elastins [55, 56]. Immune cell proteases also are capable of cleaving cytokines, growth hormone, neuropeptides, and procoagulant proteins such as Factors X and V. 

Scleroproteins. Insoluble in water and neutral solvents and resistant to enzymic hydrolysis. These are fibrous proteins serving structural and binding purposes. Collagen of muscle tissue is included in this group, as is gelatin, which is derived from it. Other examples include elastin, a component of tendons, and keratin, a component of hair and hoofs. 

In this book, he emphasized the importance of the microscopic and the submicroscopic structure of fibrous high polymers. The reactions of cellulose with water, aqueous alkalis, organic bases, ammonia, and strong salt solutions were all stressed. Special attention was given to various types of cellulose esters, to cellulose xanthate, and to the cellulose ethers. The oxidation of cellulose under a variety of conditions was described, as were the hydrolysis reactions. The latter included discussions on reversion and on the kinetics of acid hydrolysis. It is interesting to note that Heuser, who earlier had criticized the terms hydrocellulose and oxycellulose, and had... 

Partial hydrolysis of elastin by reagents other than organic acids also gives rise to a mixture of soluble proteins similar to a- and /3-elastin. Thus Wood (quoted by Hall et al, 1952) first demonstrated that partial hydrolysis with dilute sodium hydroxide yields a protein which forms a reversible coacervate on raising the temperature of its solutions. Later Wood (1958) showed that on prolonged heating in aqueous solution a-elastin is converted into an insoluble gellike form. Reconstituted fibers of heat-treated a-elastin resembled fibrous elastin in their elastic behavior and X-ray-dif-fraction pattern but imlike purified elastin they were dissolved by 1 % acetic acid at 100°C and by crystalline trypsin. 

The soluble proteins derived from elastin retain the yellow color of the fibrous protein, and also its strong blue-white fluorescence, and the pigment cannot be removed by further mild hydrolysis and exhaustive dialysis or repeated precipitation with alcohol. It thus appears that a fluores-... 

Tonoiilament Assembly. The available information suggests that keratin is sequentially assembled around primary fibers that originate within the attachment plates of desmosomes (27). The dense cores of 50-A filaments (stained with uranyl acetate) represent such fibers (64, 84). These cores and their surrounding fibrous protein probably contain about 50% a helix (71). They contain even less sulfur (32, 64) than the high methionine (1.4 residues/100 amino acid residues), low cystine (1.1 residues/100 amino acid residues) fraction obtained by Baden after partial enzymatic hydrolysis (82). Studies with tritiated amino acids suggest that basal cells preferentially incorporate methionine, leucine, and phenylalanine within their elements (73, 74). In Figure 13A the primary rope is identified with the 35-A diameter of the smallest filaments that have been isolated (32). 

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