Hexokinase with glucose

The elegant enzymatic procedure of Drawert and Kupper (59) permits determination of glucose, fructose, and (when necessary) sucrose. Glucose reacts with adenosintriphosphate (ATP) in the presence of hexokinase (HK) to produce glucose-6-phosphate. 

The inflowing glucose is phosphorylated by the enzyme hexokinase with a Km in the order of 0.1-0.2 mM [17]. It is therefore able to keep Gi low, so the net influx in practice is independent of Gj. This is, however, a truth with modifications. The activity of hexokinase is inhibited by its product G6P, so if G6P is not removed fast enough, the activity of the hexokinase goes down. 

Deoxy-D-arabtno-hexose ( 2-deoxy-D-glucose ) is not a substrate for the growth, respiration, or fermentation of yeasts. However, it is metabolized, although the extent to which the hexose ring is cleaved is small. The compound is phosphorylated by hexokinase, with ATP as the donor.3660 2-Deoxy-D-arabtno-hexose is employed as an ana-... 

In this assay, diluted serum is preincubated with glucose, hexokinase, NADP+, and G6P dehydrogenase to allow any creatine phosphate and ADP present in the serum sample to be consumed. When a constant, 4340 value is achieved, a reagent solution consisting of concentrated creatine phosphate and ADP is added, and the increase in A340 is monitored as a function of time. A typical trace is shown in Figure 3.2. The slope of the initial linear section of this curve is directly proportional to enzyme concentration. 

In the first reaction glucose reacts with ATP to produce ADP and PEP the enzyme for this first step is hexokinase the notation is similar for the remaining reaction steps, with the enzymes as indicated. The rate of influx of glucose into the system is constant. Due to the feedback mechanisms in both the PFK and PK reactions chemical oscillations of some species may occur, see Fig. 16.4. These oscillations have been observed [1] and are also obtained from numerical solutions of the deterministic mass action rate equations of the model in Fig. 16.1 for given glucose inflow conditions, see Fig. 16.4. 

Another aliquot of the extract is now treated with hexokinase plus glucose or with crayfish muscle ATPase prepared according to the method of Lohmann (11) to convert all of the ATP into ADP. This preparation is then boiled and is tested for ADP content (see Fig. 2) (17). Since the ATP content can be determined directly by the zero time extrapolation of the light curve in the previous test, the ADP present represents that initially present plus that derived from the breakdown of ATP. The sensitivity of... 

Fig. 13. Diagram of an active transport glucose-pump with permanent structure ion-selective poly anionic external valve-membrane hexokinase layer (heat sink equivalent for glucose Glucose+...

Fig. 4. Schematic of a multisequence biosensor in which the target glucose is first converted to glucose-6-phosphate, G6P, in the test solution by hexokinase. G6P then reacts selectively with glucose-6-phosphate dehydrogenase immobilized on the quartz crystal surface. Electrons released in the reaction then chemically reduce the Pmssian blue film (see Fig. 3), forcing an uptake of potassium ions. The resulting mass increase is manifested as a...

Figure 19-5. Variation in glucose phosphorylating activity of hexokinase and glucokinase with increase of blood glucose concentration. The for glucose of hexokinase is 0.05 mmol/L and of glucokinase is 10 mmol/L.

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