D-Fructose in Testes and Spermatozoa

Biosynthetic Pathway for Production of D-Fructose in the Accessory Reproductive Organs 

Considerable effort has been devoted to elucidating the biosynthetic pathway for the production of D-fructose from D-glucose. Two pathways for biosynthesis in seminal vesicles have been proposed. The 

In the absence of D-glucitol, incubated, washed, ram spermatozoa convert about 20% of the D-fructose present into D-glucitol.91 In the presence of low concentrations of D-glucitol, the conversion of D-fructose into D-glucitol is depressed, and, when the D-fructose to D-glucitol ratio is 3 1, D-fructose is converted quantitatively into lactate, with no D-glucitol produced. D-Fructose is used in preference to D- 

The ratio [NADH]/[NAD] controls the formation of D-fructose. The ratio is low in cytosol, leading to a concentration of seminal D-fructose derived from blood D-glucose without energy expenditure beyond that required to maintain a favorable ratio of the nicotinamide nucleotides.92 

Spermatozoa in ejaculated, mammalian semen are unusual in their considerable reliance on the metabolism of D-fructose, the principal 

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