Glucose critical values

Li P A, Shamloo M, Katsura K et al 1995 Critical values for plasma glucose in aggravating ischaemic brain damage correlation to extracellular pH. Neurobiology of Disease 2 97-108... 

Isolated Enzymes and Other Biocatalysts. As mentioned above, isolated enzymes fall under the biocatalyst domain. Purified enzymes probably will not play as large a role as microorganisms in commodity chemicals production fiom biomass, largely because of the impracticality of preparing all of the many enzymes necessary to convert glucose to a useful chemici. Purified enzymes will have an impact, however, in the pharmaceutical and fine chemicals industries, where a critical, value-added downstream step needs to be performed. 

In the process of the cultivation of recombinant E. coli, low yields are observed due to the formation and accumulation of acetic acid resulting from overflow metabolism. Thus, it is necessary to prevent and monitor the formation of acetic acid, which can be avoided by the introduction of glucose to the medium. However, the rate of glucose addition must be monitored in order to maintain the growth below a critical value. In this context, a flow injection system was developed for the determination of acetic acid in E. coli cultivations with electrochemical detection based on immobilized AK, PK, and LDH, with amperometric detection of NADH. A limitation associated with this system was that the enzyme AK lost 90% of its activity after only one fermentation. The authors thus suggested that, due to the low stability of immobilized AK in the fermentation measurements, alternative enzymes needed to be found (Tang et al., 1997). 

Compounds absorbed by active uptake mechanisms (e.g., glucose and Gly-Pro) and compounds known to be substrates for efflux transport (e.g., digoxin, verapamil) were also included in the list. The applied concentration (10-500 pM) only had minor effects on the permeability values. Thus, the choice of concentration was not critical for this set of compounds with respect to the relationship between permeability and fraction absorbed in humans. Changing the pH on the apical donor side had significant effects on the Papp values of several compounds, the effects being in agreement with the acid-base properties of the compounds. The... 

Two important inferences may be drawn from Figs. 1 and 2. (1) The maximum mobilities of the carbohydrates are generally in the pH region 9-10 and, consequently, borate buffers within this range are usually selected for zone electrophoresis. (2) The relative mobilities of certain pairs of carbohydrates may be critically dependent on pH for example, at pH 9-10, D-glucose has a mobility greater than that of D-fructose, whereas, at pH 7-8, the reverse relationship obtains. Thus, careful selection of an appropriate pH may be of value in facilitating certain separations. 

The problem of crystal reactivity and diffusion limitations has been considered in detail by Makinen and Fink [170]. They provide a simple treatment for crystals approximated as a plane sheet of material which leads to the definition of a limiting crystal thickness below which kinetic measurements of second-order rate constants are not affected by rate-limiting diffusion processes. For papain [172], ribonuclease A [173] and deoxyhaemoglobin [174], where the crystal thicknesses are comparable to the critical crystal thickness, reactivities are the same in the crystal and solution. In the case of glycogen phosphorylase b Kasvinsky and Madsen [175] demonstrated that the values for both substrates, glucose 1-phosphate (37 + 8mM) and malto-heptaose (176 + 20 mM), were the same in the crystal and solution. The 10-100-fold reduction in rate, despite the fact that crystal thickness was only twice the critical thickness, may be attributable partly to the allosteric nature of this enzyme and partly to the fact that the large substrate maltoheptaose (molecular weight, 1152) may not obey the simple diffusion rules in the crystal. 

Chlorogenic acid Tannic acid Gallic acid Hesperiden Rutin Catechol Glucose Naphthalene Exp Xi = Experimental value in water 20 C Cal c X2= Calculated value in sub-critical water 120 C... 

If cellulose does not provide fuel value, we must conclude that it is not converted in the body into CO2 and H2O, as starch is. A slight but critical difference in the structures of starch and cellulose explains why only starch is broken down into glucose in the body. Cellulose passes through without undergoing significant chemical change. It serves as fiber, or roughage, in the diet but provides no caloric value. 

---