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The seminal fluid contains fructose as the main energy source for the sperm and not glucose.

Why is fructose and not glucose the primary energy source for these sperm, since glucose is the preferred energy source for most other tissues?

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I am not sure this is a very reliable source but it does seem logical. –  biogirl Nov 12 '13 at 17:54
    
@biogirl Not all answers there are reliable, but this one seems to be genuine. But you never can tell without a good reference. –  Satwik Pasani Nov 13 '13 at 2:04
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i am not very sure about this but perhaps since glucose is preferred source for other cells, fructose is allotted to sperm so that other cells dont compete for it.. totally a wild guess because I dont know of any other reason. <plus fructose is not influenced by insulin. but i dont see how it fits here> –  WYSIWYG Nov 13 '13 at 4:54
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FYI : Seminal vesicle is the only place in the body where fructose is secreted. –  biogirl Nov 14 '13 at 16:58

1 Answer 1

up vote 5 down vote accepted

I have been searching this for a while and I got something of an answer, which I am posting below.

There are primarily two advantages of using the polyol pathway and aldose reductase to produce fructose from glucose via sorbitol:-

1) Quoting the book here,

Seminal fluid contains up to 11 mmol/L (200 mg/dl) of free fructose. It is the major energy source for the sperm cells in their all-important race for the ovum. The advantage of fructose over glucose may be that many bacteria, which compete with the sperm cells for the available nutrient, prefer glucose to other energy sources.

Thus, to avoid other competitive bacteria and cells from utilising the energy source of sperm, fructose is used as the energy source since the bacteria prefer glucose.

2)Another reason is that the metabolism of sorbitol into fructose is energetically efficient way (no ATP required) as compared to glycolytic conversion of glucose into fructose(G$\rightarrow$G6P$\rightarrow$F6P$\rightarrow$F). Tapping the polyol pathway is energetically preferred to metabolizing fructose produced during glycolysis.This is only to show the possible evolution of the polyol pathway once the advantage of using fructose as the energy source was established. It does not explain why the fructose was advantageuos but just that if it was advantageous, the semen-producers would develop the currently existing machinery to produce fructose as the exclusive source of energy.

Hence, sperms (seminal secretion) contains fructose as the primary energy source and not glucose.

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Neither of these arguments make sense to me. Firstly, if there was an advantage to using fructose amongst bacteria that might encounter semen then they would evolve to exploit the niche. I note that E. coli for example will quite happily use fructose as C source. On the second point, I don't see how the fact that you can make fructose from glucose without using ATP is an argument against just using glucose in the first place. In any case I think that arguments from energetic efficiency are rarely convincing. –  Alan Boyd Nov 15 '13 at 16:13
    
@AlanBoyd The second argument is only to show the possible evolution of the polyol pathway once the advantage of using fructose as the energy source was established. It does not explain why the fructose was advantageuos but just that if it was advantageous, the semen-producers would develop the currently existing machinery to produce fructose as the exclusive source of energy. –  Satwik Pasani Nov 15 '13 at 17:36
    
@AlanBoyd The first argument, though not substantial in its claims, is the only one I could come up with. If you do know an alternative argument, I would be most happy to consider it and accept it as an answer. –  Satwik Pasani Nov 15 '13 at 17:38
    
I admit that I have not come up with an answer, but it seems to me that maybe there is something else about fructose that makes it a better choice. Maybe it has some function, other than as a C source, in the fluid. It may be relevant that it is much more soluble than glucose, although the concentration that you quote is way below the solubility limit for either sugar. –  Alan Boyd Nov 15 '13 at 17:46

protected by Chris Dec 13 at 10:15

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