Time enzymatic conversion

A Box-Behnken design was employed to investigate statistically the main and interactive effects of four process variables (reaction time, enzyme to substrate ratio, surfactant addition, and substrate pretreatment) on enzymatic conversion of waste office paper to sugars. A response surface model relating sugar yield to the four variables was developed on the basis of the experimental results. The model could be successfully used to identify the most efficient combination of the four variables for maximizing the extent of sugar production. 

The high specificity required for the analysis of physiological fluids often necessitates the incorporation of permselective membranes between the sample and the sensor. A typical configuration is presented in Fig. 7, where the membrane system comprises three distinct layers. The outer membrane. A, which encounters the sample solution is indicated by the dashed lines. It most commonly serves to eliminate high molecular weight interferences, such as other enzymes and proteins. The substrate, S, and other small molecules are allowed to enter the enzyme layer, B, which typically consist of a gelatinous material or a porous solid support. The immobilized enzyme catalyzes the conversion of substrate, S, to product, P. The substrate, product or a cofactor may be the species detected electrochemically. In many cases the electrochemical sensor may be prone to interferences and a permselective membrane, C, is required. The response time and sensitivity of the enzyme electrode will depend on the rate of permeation through layers A, B and C the kinetics of enzymatic conversion as well as the charac-... 

FIGURE 6.47 Chromatogram overlays obtained for 19 time points during evaluations described in text. S denotes substrate. P denotes product. Observed levels of enzymatic conversion are indicated as slow, medium fast, and optimal for a particular application. 

A major advantage of biosynthesis is the fact that many enzymatic conversions have been evolved, working under almost the same reaction conditions. With the present knowledge of many biosynthetic pathways we now also have the heritage of many powerful bioconversions that, by far, work at ambient temperature and pressure and in aqueous medium. In other words, it is time to fully exploit biosynthetic procedures and the possibility of combining them with appropriate or new chemocatalytic transformations in a cascade mode of conversion. 

This study shows that steam pretreatment is an efficient method to increase the enzymatic accessibility of the water-insoluble, cellulose-rich component in corn stover. After pretreatment, the enzymatic conversion from cellulose to glucose increased nearly four times, compared to the untreated corn stover. 

Trypsin-encapsulated sol-gel (alkoxysilane-based) was fabricated in situ onto the sample reservoir of a PMMA chip. This was employed for enzymatic conversion of NBD-labeled ArgOEt and bradykinin, followed by CE separation of the products. The enzymatic activity of the encapsulated trypsin as given by the Km value was found to be 19 times higher than that of the free trypsin. The stability of trypsin was 1 week at 4°C. This enhanced enzyme stability was possibly caused by the prevention of enzyme autolysis by the sol-gel matrix [1062],... 

A great amount of time, money and effort is being devoted to the use of cellulose as a feedstock for the production of ethanol. The studies incorporate chemical or enzymatic conversion of the cellulose to glucose and the conversion of this to ethanol with yeast (Saccharomyces) or bacteria (Zymomonas). However, a third process is presently under development at Massachusetts Institute of Technology whereby the direct conversion of cellulose to ethanol is being attempted without a separate hydrolysis step. ... 

As mentioned above, this process now serves mainly as an adjunct to enzymatic conversion of starch and is rarely used alone. A starch slurry containing 35-45 percent solids is acidified with hydrochloric acid to about pH 1.8-1.9. The suspension is pumped into an autoclave (converter) where live steam is gradually admitted to a pressure of 30-45 psi. The conversion time largely determines the DE of the hydrolyzate for example, eight min... 

AFEX [Ammonia Fiber Explosion (or Expansion)] A pretreatment process for ligno-cellulose prior to enzymatic conversion to ethanol. The wood is exposed to liquid ammonia at 60 to 100°C for a short time, and the pressure suddenly released. Invented in 1998 by B.E. Dale and M. Moniruzzaman at Texas A M University and further developed by Dale at Michigan State University. In 2006, AFEX was regarded as the leading nonenzymatic biomass pretreatment process. 

While in the presence of 2-oxoglutaric acid neither decarboxylation nor acyloin condensation had been observed, as expected from previously published results (75), we succeeded in the enzymatic conversion of the mono ethyl ester 3 to ethyl 4-oxobutanoate 4, using both whole yeast cells (Saccharomyces cerevisiae) and purified PDC. The oxo ester 4 served as substrate for a second reaction catalyzed by PDC. Formation of a new carbon-carbon bond was accomplished in the presence of pyruvic acid which acted as donor of a C2-unit. Thus, ethyl 4-hydroxy-5-oxohexanoate 5 was obtained for the first time as the result of an enzymatic acyloin condensation. Finally, traces of acid induced the lactonization of hydroxyester 5, indicating it as direct precursor of solerone 1 (Figure 1). 

The absorption and distribution of 1,4BD is similar to that of GHB. It is a lipophobic or polar compound so it does not absorb faster than GHB. After its absorption, it requires a two-step enzymatic conversion to GHB that results in a slightly longer time to peak GHB concentration and also a longer time of elevated GHB concentration. The conversion process of 1,4BD to GHB can be slowed or inhibited by ethanol, pyrazole or disulfiram. 

Higher yield and lower costs of production can be achieved if the enzymatic conversion is performed in the presence of toluene at appropriate pH, temperature and reaction time. The main product is P-CD, since it forms an insoluble complex with toluene (Figure 16.5). The complex formation drives the conversion of starch towards the synthesis of the precipitated CD, thus enriching its content in the final mixture of products. The continuous removal of P-CD from the system shifts the equilibrium in favor of the product. 

Enzymes exhibit their highest activity at temperatures appreciably higher than those required for microbial fermentations. When such differences are negligihenzymatic hydrolysis and fermentation can simultaneously occur. Provided that enzyme concentration is high enough to prevent enzymatic conversion from being rate limiting, fermentation time and capital costs can be reduced. 

There is no final consensus on whether procyanidin biosynthesis is controlled thermodynamically or enzymatically. In either case proanthocyanidins are synthesized through sequential addition of flavan-3,4-diol units (in their reactive forms as carbocations or quinone methides) to a flavan-3-ol monomer [218]. Based on the latest findings there is some evidence that different condensation enzymes might exist which are specific for each type of flavan-3,4-diol [64] and that polymer synthesis would be subject to a very complex regulatory mechanism [63]. But so far, no enzyme synthetase systems have been isolated and enzymatic conversion of flavanols to proanthocyanidins could not be demonstrated in vitro [219]. If biosynthesis was thermodynamically controlled, the variation in proanthocyanidin composition could be explained by synthesis at different times or in different compartments [64], The hypothesis of a thermodynamically controlled biosynthesis is based on the fact that naturally and chemically synthesized procyanidin dimers occur as a mixture of 4—>8 and 4—>6 linked isomers in approximate ratios of 3-4 1 [220]. Porter [164] found analogous ratios of 4—>8 and 4—>6 linkages in proanthocyanidin polymers. 

Drugs used for hypertension that have markedly delayed effects are those that have effects at the nerve terminus level. This drug could be guanethidine or reserpine, but, because effects are not seen before the trace is truncated, it is likely to be a-methyldopa, because the drug requires time for the enzymatic conversion to a-methylnorepinephrine before antihypertensive effects are seen. 

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