Enzyme utilization efficiency

Figure 2. Effect of superficial velocity on enzyme utilization efficiency. Reactor size diameter—47 mm, thickness—0.45 mm, weight—0.43 g. Conditions pH— 7.5, temperature—60°C. Substrate dextrose—45% w/v, MgSOf 7HiO—2 g/L,...

The differences in the rate constant for the water reaction and the catalyzed reactions reside in the mole fraction of substrate present as near attack conformers (NACs).171 These results and knowledge of the importance of transition-state stabilization in other cases support a proposal that enzymes utilize both NAC and transition-state stabilization in the mix required for the most efficient catalysis. Using a combined QM/MM Monte Carlo/free-energy perturbation (MC/FEP) method, 82%, 57%, and 1% of chorismate conformers were found to be NAC structures (NACs) in water, methanol, and the gas phase, respectively.172 The fact that the reaction occurred faster in water than in methanol was attributed to greater stabilization of the TS in water by specific interactions with first-shell solvent molecules. The Claisen rearrangements of chorismate in water and at the active site of E. coli chorismate mutase have been compared.173 It follows that the efficiency of formation of NAC (7.8 kcal/mol) at the active site provides approximately 90% of the kinetic advantage of the enzymatic reaction as compared with the water reaction. 

The reasons for the increasing acceptance of enzymes as reagents rest on the advantages gained from utilizing them in organic synthesis Isolated or wholecell enzymes are efficient catalysts under mild conditions. Since enzymes are chiral materials, optically active molecules may be produced from prochiral or racemic substrates by catalytic asymmetric induction or kinetic resolution. Moreover, these biocatalysts may perform transformations, which are difficult to emulate by transition-metal catalysts, and they are environmentally more acceptable than metal complexes. 

In contrast to zinc, the crucial role of Fe in the bioenergetics of carbon (C) and N metabolism is well recognized (e.g., Morel et al., 1991 Sunda, 1989). Substantial amounts of Fe are required in both photosynthetic and respiratory electron transport chains (e.g., Raven, 1988), the synthesis of chlorophyll (Chereskin and Castelfranco, 1982), and the assimilation ofNOj. Theoretical calculations based on Fe utilization efficiencies and cellular metabolic Fe demands, predict that phytoplankton growing on NOJ require 60% more Fe than those growing on NH (Raven, 1988, 1990), and greater cellular Fe requirements for NO growth have indeed been demonstrated for laboratory cultures of diatoms (Maldonado and Price, 1996). The extra Fe is needed to reduce NO to NH4 before it can be incorporated into amino acids. This process requires the assimilatory enzymes nitrate reductase (requires one... 

The mechanism of an actual hydrolysis reaction catalyzed by this prototype phosphomonoesterase has never been studied stereochemically. This apparent omission is presumably explained by the very low catalytic efficiency of the enzyme toward phosphorothioate monoesters as compared to phosphate monoesters (75) certainly, chiral [ O, 0]phosphorothioate 0-ester substrates already exist, and methodology is available for the configurational analysis of the chiral [ 0, 0, 0]thiophosphate that would be produced if the chiral substrate were hydrolyzed in H2. In fact, the low catalytic reactivity of phosphorothioate O-esters and the high reactivity of phosphorothioate S-esters has been explained by the enzyme utilizing nucleophilic catalysis (an associate mechanism) to achieve hydrolysis of the phosphate ester bond 40). 

S (phosphate)n + D-glucose <1-13> (<1> i.e. poly(P)n, no substrates are monophosphate, diphosphate or triphosphate [2] <1>, no utilization of triphosphate or tetrapolyphosphate [1] <11> the enzyme utilizes polyphosphate much more efficiently than it does ATP, with a turnover num-ber/Kpolyphosphate to turnover number/KATP ratio of 2800 [8] <8> polyphosphate is utilized nonprocessively with a preference for longer chains [9]) (Reversibility ir <12,13> [11,12] <1-11> [1-10]) [1-12]... 

To illustrate the efficiency of enzyme utilization with this microporous enzyme support, 30 g of support material was immobilized with 22,000 IGIU of purified enzyme. The resulting reactor had an expressed activity of 726 IGIU/g at 60 C. A 40% w/w solution of 99% pure dextrose containing 2 g/1 MgS04 7H20 and 1 g/1 of NaHC03 at pH 7.5 was converted to a 45% fructose product in 6.5 min and an equilibrium product of approximately 50% fructose in less than 12 min residence time. The flow rate required to obtain a 45% converted product was 6 ml/min. 

Although naringenin has been established as the natural product of the synthase from parsley because 4-coumaroyl-CoA was the only substrate utilized efficiently (Hrazdina et al., 1976), production of eriodictyol (5,7,3, 4 -tetrahydroxyflavanone) (XIX) from caffeoyl-CoA and malonyl-CoA by a similar enzyme from H. gracilis was pronounced at a lower pH (6.5-7.0). Naringenin formation had a pH optimum of 8.0 (Saleh et al., 1978). Ligase enzymes responsible for the activation of appropriate acids to their CoA derivatives have been isolated from parsley (Knobloch and Hahlbrock, 1977) and a variety of plant tisues (Gross and Zenk, 1974 Knobloch and Hahlbrock, 1975) and require ATP, CoA, and Mg " " as cofactors. 

Monte JR, Brienzo M, Milagres AMR Utilization of pineapple stem juice to enhance enzyme-hydrolytic efficiency for sugarcane bagasse after an optimized pre-treatment with alkaline peroxide. Appl Energy 2011 88 403-8. 

A wide variety of animal species are subjected to the administration of drugs during their lifetime.The various animal species can encounter drugs and other dietary additives by different routes and this is dependent on the environment in which they are kept. Intensively reared animals tend to have considerable consistency in the components of their diets and thus are much less likely to encounter the range of naturally produced compounds that extensively produced animals encounter. The desire for less expensive dietary constituents and increased efficiency of use has induced feed manufacturers and producers to add enzyme supplements to diets of most farmed animals to reduce the negative effects of indigestible dietary carbohydrates, refactory proteins and unavailable minerals such as phosphorus. This use of dietary additives to improve nutrient utilization and environmental consequences of feeding animals intensively has been the subject of intense research activity in the last five years. " The... 

The class A enzymes have Mx values around 30,000. Their substrate specificities are quite variable and a large number of enzymes have emerged in response to the selective pressure exerted by the sometimes abusive utilization of antibiotics. Some of these new enzymes are variants of previously known enzymes, with only a limited number of mutations (1 4) but a significantly broadened substrate spectrum while others exhibit significantly different sequences. The first category is exemplified by the numerous TEM variants whose activity can be extended to third and fourth generation cephalosporins and the second by the NMCA and SME enzymes which, in contrast to all other SXXK (3-lactamases, hydrolyse carbapenems with high efficiency. Despite these specificity differences, the tertiary structures of all class A (3-lactamases are nearly superimposable. 

Further examples of the utility of the allylic sulfoxide-sulfenate interconversion in the construction of various biologically active natural products include intermediates such as the /Miydroxy-a-methylene-y-butyrolactones (e.g. 63)128 and tetrahydrochromanone derivative 64129. Interestingly, the facility and efficiency of this rearrangement has also attracted attention beyond the conventional boundaries of organic chemistry. Thus, a study on mechanism-based enzyme inactivation using an allyl sulfoxide-sulfenate rearrangement has also been published130 131. 

In the enzyme design approach, as discussed in the first part of this chapter, one attempts to utilize the mechanistic understanding of chemical reactions and enzyme structure to create a new catalyst. This approach represents a largely academic research field aiming at fundamental understanding of biocatalysis. Indeed, the invention of functional artificial enzymes can be considered to be the ultimate test for any theory on enzyme mechanisms. Most artificial enzymes, to date, do not fulfill the conditions of catalytic efficiency and price per unit necessary for industrial applications. 

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