Sensing fructose

In clinical chemistry however, these systems have not been differentiated as yet. Since the oxidation of an alcohol corresponds to the reduction of a ketose or an aldose, the designations ketose reductase and aldose reductase, respectively, were suggested (H4, W14). In this paper however, the enzyme or enzyme system will be named polyol or sorbitol dehydrogenase (SDH), although the latter expression does not characterize exacdy the enzyme s function in a general biochemical sense. But sorbitol or fructose have been commonly used as substrates in clinical chemical investigations. 

Sucrose is rapidly dissociated into glucose and fructose by the enzymes in your mouth and in your stomach, and your taste receptors sense sweetness. A problem (for Coca Cola) is that fructose tastes five times as sweet as glucose so 40% of the sucrose they purchase is wasted compared to pure fructose. A problem for you is that both sugars have the same calories, and the soft drink companies want to advertise lower calories for an aceeptable sweetness. 

It is to be noted that when a and / are attached to some iso-propylidene ketals of fructose they are part of a trivial name and are not used in the customary anomeric sense the quotation marks may serve for easy distinction. 

The direct electronic communication of this series of redox enzymes allows their application as bioactive sensing interfaces p-cresol [12], methylamine [14] and fructose [ 15] detection have been reported in the presence ofp-cresol methyl hydroxylase, methylamine dehydrogenase and fructose dehydrogenase, respectively. 

Fig. 15.2 Flow injection set-up for optical sensing and screening library members and competitive binding assay for fructose developed on-bead using fluorescent labeled glucose...

Non-enzymic aldose-ketose isomerisations that are acid catalysed appear to involve a 1,2-hydride shift. During acid-catalysed rearrangement of glucose to fructose, the label of [2- H]glucose substrate is retained in the [l- H]fructose product, distributed equally between the proR and proS positions." In the reverse sense retention of the label of tritiated fructose in the glucose and mannose products was not complete. Similar observations were made for the xylose-xylulose interconversion." With an appropriate sugar configuration (ribose), even the base-catalysed reaction proceeds partly with retention of label, presumably by the same mechanism as with trioses. 

Figure 6.63 Substrate activation mechanisms and stereochemistry (shown in the sense of ketone reduction) for (a) aldose reductases, (b) long-chain dehydrogenases, (c) glucose-6-phosphate dehydrogenase and (d) sorbitol dehydrogenase. The glutamate ligand to Zn is shown removed in the complex with fructose, but this is speculative.

Fructose crystallizes well when pure. It is much more soluble and considerably sweeter than common sugar. It is a physiological sugar in every sense of the word. Now that we have analytical methods capable of distinguishing fructose from glucose certainly, it has been shown that fructose is normally present in human blood (71). In embryonic and newborn infants, the level is much higher than in adults (5). Fructose is also the predominant sugar of seminal fluid and its concentration has an important effect upon the motility of spermatozoa (38). 

In contrast, other tastes including sweetness (as in sucrose, fructose, and artificial sweetener) are sensed by actually binding to specific membrane receptor proteins in taste receptor cells. The chemicals sensed as sweet bind to selective sites on a membrane receptor in a lock-and-key fashion (im-... 

Many other similar applications have been reported such as the electrochemical determination of electroinactive cationic medicines,313 determination of urea,314 uric acid,315 and application to glucose biosensors to decrease interference of ascorbate, urate, and acetaminophen.316 Enzyme immobilized membranes are also sensing membranes, e.g. urea responsive membranes, poly(carboxylic acid) membranes in which urease is immobilized,317 fructose responsive membranes, and polyion complex membranes in which fructose dehydrogenase is immobilized.318 Such applications will expand further in the future and contribute to human life. 

Blass, E. M. Shide, D. J. 1994. Some comparisons among the calming and pain-relieving effects of sucrose, glucose, fructose and lactose in infant rats. Chem. Senses 19, 239-249. 

Electroen matic Sensing of Fructose Using Fructose Dehydrogenase Immobilized in a Self-Assembled Monolayer on Gold... 

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