Enzymes, rigidity

Table 2 shows half-life time and inactivation coefficient for YLL soluble and immobilized on different supports. The enzyme immobilized on MANAE-agarose support presented lower stability than the soluble enzyme, perhaps because the immobilized derivative has been prepared in the presence of detergent to ensure the enzyme desegregation could be monomers, while soluble enzyme as dimers [27, 28]. Random immobilization may not really improve enzyme rigidity even in some cases, the enzyme stability may decrease after immobilization [10-14], e.g., if the support is able to establish undesired interactions with the enz)une. 

Polyalcohols, such as glycerol, sugar, sorbitol, and propylene glycol may prevent denaturation (28). Also substrates or substrate analogues often stabilize by conferring an increased rigidity to the enzyme stmcture. 

The Immobili dEn me System. The glucose isomerases used are immobilized and granulated to a particle size between 0.3 and 1.0 mm. The enzyme granulates must be rigid enough to withstand compaction when they are packed iato the column. Ca " acts as an inhibitor in the system, and therefore calcium salts need to be removed from the feed symp. Conversely, Mg " acts as an activator, and magnesium salts are added to the feed symp. 

Pioneering enzyme specificity studies at the turn of the century by the great organic chemist Emil Eischer led to the notion of an enzyme resembling a lock and its particular substrate the key. This analogy captures the essence of the specificity that exists between an enzyme and its substrate, but enzymes are not rigid templates like locks. 

The nature of the penicillin derivatives accessible by this "feeding" route was severely limited by the fact that the acylat-ing enzyme of the Penicillium molds would accept only those carboxylic acids which bore at least some resemblance to its natural substrates. A breakthrough in this field was achieved by the finding that rigid exclusion of all possible side-chain substrate from the culture medium afforded 6-APA as the main fermentation... 

Epoxides are found in thousands of biological molecules and constitute vital functional entities. They can impart localized structural rigidity, confer cytotoxicity through their role as alkylating agents, or act as reactive intermediates in complex synthetic sequences. The widespread occurrence of epoxides is contrasted by only a handful of aziridines that are known to date. In this chapter we would like to introduce the different mechanisms by which enzymes produce epoxides. 

Pyruvic acid is an intermediate in the fermentation of grains. During fermentation the enzyme pyruvate carboxylase causes the pyruvate ion to release carbon dioxide. In one experiment a 200.-mL aqueous solution of the pyruvate in a sealed, rigid 500.-mL flask at 293 K had an initial concentration of 3.23 mmol-L -l. Because the concentration of the enzyme was kept constant, the reaction was pseudo-first order in pyruvate ion. The elimination of CU2 by the reaction was monitored by measuring the partial pressure of the C02 gas. The pressure of the gas was found to rise from zero to 100. Pa in 522 s. What is the rate constant of the pseudo-first order reaction ... 

Several reports have indicated that enzymes are more thermostable in organic solvents than in water. The high thermal stability of enzymes in organic solvents, especially in hydrophobic ones and at low water content, was attributed to increased conformational rigidity and to the absence of nearly all the covalent reactions causing irreversible thermoinactivation in water [23]. 

Early in the last century, Emil Fischer compared the highly specific fit between enzymes and their substrates to that of a lock and its key. While the lock and key model accounted for the exquisite specificity of enzyme-substrate interactions, the imphed rigidity of the... 

Information generally flows from DNA to mRNA to protein, as illustrated in Figure 40-1 and discussed in more detail in Chapter 39. This is a rigidly controlled process involving a number of complex steps, each of which no doubt is regulated by one or more enzymes or factors faulty function at any of these steps can cause disease. 

Reagents. The measurement of enzyme activities requires rigid control of the analytical conditions, including accurate measurement of reagent and sample volumes, and careful control of temperature, pH and reagent stability. 

And third, since virtually all enzymes [67], particularly those that catalyze phos-phoryl-transfer reactions [68 74], possess structures with at least two, discrete, relatively rigid structural domains, or lobes, separated by a deep cleft, the cytoplasmic portion of the H -ATPase polypeptide chain in the model of Fig. 2 is drawn in such a way as to suggest this situation. The proposed interdomain cleft is indicated by the arrow. No additional structural features of the ATPase molecule are implied in the model. In regard to comparisons with the Ca -ATPase, it is of interest to note that the two cytoplasmic domains proposed in Fig. 2 correspond to the Cl and C2 domains in the model of Andersen and Vilsen [53]. 

Thermostability of enzymes increases in apolar organic solvents increasing the stability and rigidity of the molecules. This effect is probably due to low-water activity [130]. 

C. Allow for Flexibility in the Design of Enzyme Inhibitors to Assure Optimal Fit in an Often Rigid Active Site Cavity... 

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