Cellular respiration in sperm cells.

[MrMistery]

I know that sperm cells use fructose in cellular respiration and not glucose. My question is HOW? The first step of glycolysis consists of attaching a phophate to glucose, catalyzed by the enzyme hexokinase. The second step consists of isomerization of glucose-6-phosphate to fructose-6-phosphate catalyzed by phosphoglucoisomerase.
My question is: Can hexokinase also catalyse the addition of the phophate group to fructose and it simply skips phase 2? Seems improbable as we know enzymes are super specific.
And, if it is so, why dis the living world evolve to use glucose and not fructose? It would much easier to use fructose if this was possible since fructose is the first hexose formed in photosinthesis...

[victor]

the answer is in the organic chemie book..wait for a moment, I'll find it for you....I think this question is just the same with, "why our body use PGAL instead of dihydroxyasetone derived from fructose-1,6-diphosphate??"

[zami'87.]

Fructose metabolism by mature boar spermatozoa
A. R. Jones and D. E. Connor
Abstract
In 1945, Mann showed fructose to be the principal sugar in semen. For over half a century the means by which fructose is metabolized by sperm has been assumed to be by an initial phosphorylation catalysed by hexokinase, but this has never been substantiated. In the present study, by comparing the metabolism of glucose and fructose by both whole boar sperm and hypotonically treated cells, it is confirmed that fructose is phosphorylated by hexokinase to produce fructose 6-phosphate.
Keywords: hexokinase, hypotonically treated sperm.

Reproduction, Fertility and Development 12(8) 355 - 359


........

Two hexokinases of Homarus americanus (lobster), one having great affinity for mannose and fructose and low affinity for glucose.
Hexokinase I appears to be different from any animal hexokinase previously described. It has a high affinity for mannose and fructose and low affinity for glucose.


so not all hexokinases use glucose as substrat


unfortunately that's all I found..maybe to ask it on chemistry forum
http://www.chemicalforums.com/

[victor]

Wow...new things for me...now, we've known that enzymes aren't that specific...

[MrMistery]

Good enough for me... Thanks zami... I understand now where my error was. Hexokinase is not an enzyme, but a family of enzymes. But my other question remains... If this is possible, why so we use glucose? Is it because it is easier to store?

[2810712]

Is glucose more stable? or is it ,as MrMistery said, easy to store[ why?]

It may be like RNA world to DNA world , i mean from fructose world to glucose world with a less imp. of fructose...
may be not... may be...





hrushikesh

[MrMistery]

Well, glucose can be polimerised to form starch and glicogen. I don't know if fructose can(sugars are still a long way to go in my chem class)

It could be like RNA->DNA, but much more evidence is needed to back up a claim like this...

[zami'87.]

Some plants synthesize fructan-a polyfructose molecule(artichoke,chicory,banana...).Kind of fructan-inulin is used in diet and has beneficial effect on health(on microflora,reduce colon cancer...). Enzymes in small intestine can't break down fructan so it acts as laxative..

[zami'87.]

Some plants synthesize fructan-a polyfructose molecule(artichoke,chicory,banana...).Kind of fructan-inulin is used in diet and has beneficial effect on health(on microflora,reduce colon cancer...). Enzymes in small intestine can't break down fructan so it acts as laxative..

further....


Function of fructans
Plants with fructans are especially abundant in areas with seasonbound or sporadic rainfall in an annual cycle (Hendry and Wallace, 1993). It could be that the evolutionary meaning of fructanaccumulation is a adaptation to drought. That is, fructans are soluble in water in contrast with starch, and is therefor osmotically active. By changing the DP of the fructans in the vacuole, the plant can quickly change the osmotic potential of it's cells without having to alter the total amount of carbohydrates. It has been shown that transgenic tobacco plants transformed with CPY-LS (a construct containing the bacterial gene levansucrase to produce fructan), put under polyethyleneglycol-mediated drought stress, had an increased growth rate, fresh weight and drought weight over wildtype plants (Pilon-Smits et al., 1995) There are also indications that this osmotic activity of fructans is involved with cold-stress. Incontrovertible evidence for another possible function than that of storage sugar of fructan is still not found.

Applications
Fructans can be applied in the foodindustry and in other industries, for example as washsoftener or biologically degradable plastics. You can already buy dairy-products with inulins. Fructans can also be used as low calory sweeteners. Humans are not able to degrade fructans, but they do have a sweet taste. Also the fructose which is produced by the degradation of fructan can be used as low calory sweetener. Fructose is 1.6 times as sweet than glucose. Fructans can also be used as substrates in the production of ethanol or glycerol for example. As source for the production of fructans, plants or bacteria can be used. At this point inulin production from cichory is the only profitable, and applied application. Disadvantages of existing fructanflora are the low degree of polymerization and the degradation in storage. On top of that chichory has a low harvest index (harvestable weight per plant) compared to the more widespread agricultural crops like patato of tabacco. It would be desirable to introduce fructanaccumulation in agricultural crops. By introduction of bacterial genes accumulation of fructans with a high DP, that were not degraded by the plants, is achieved in tabacco and in patato. This is what the research in Utrecht is about. Next to use for industrial production of fructans, there might be interesting applications possible for these transgenic plants in agriculture. Fructan accumulation can be used to achieve a higher dryweight of harvestable parts of plants. Fructan accumulation might also give drought tolerance, or cold resistance to crops. From a scientific point of view transgenic fructanaccumulating plants are interesting for research in the function of fructans in plants and the effect on carbohydrate metabolism due to the introduction of fructans.


Dig Zami dig

[MrMistery]

Something that that article doesn't mention is fructose is widely used to make sweets for people with diabethes. I have a friend who has this desease, and can only eat those special kind of sweets(they are more expensive). It is true that they have fewer callories.

Now, from what i understand of zami's article, those fructans are not produced by plants naturally, the plants have been genetically altered to produce them...

[canalon]

Something that that article doesn't mention is fructose is widely used to make sweets for people with diabethes. I have a friend who has this desease, and can only eat those special kind of sweets(they are more expensive). It is true that they have fewer callories.

Two things with fructose used by diabetics:
- First it doesn't affect glycemia like glucose (of course) so the concentration of glucose in blood raise slower and hence there is less peaks in blood sugar concentration
- Second since it is 1,2 times sweeter (in the sense of taste) than glucose you need to use less to get the same tatse, so it event reduce the numbers of calories for a given sweetness. Just like artfificial sweeteners, but much less effective

[Dr.Stein]

I already explained this somewhere I forgot where