FIGURE 18-17 Conversions of one-carbon units on tetrahydrofolate.

The different molecular species are grouped according to oxidation state, with the most reduced at the top and most oxidized at the bottom. All species within a single shaded box are at the same oxidation state. The conversion of N5,N10-methylenetetrahydrofolate to N5-methyltetrahydrofolate is effectively irreversible. The enzymatic transfer of formyl groups, as in purine synthesis (see Fig. 22-33) and in the formation of formylmethionine in prokaryotes (Chapter 27), generally uses N10-formyltetrahydrofolate rather than N5-formyltetrahydrofolate. The latter species is significantly more stable and therefore a weaker donor of formyl groups. N5-formyltetrahydrofolate is a minor byproduct of the cyclohydrolase reaction, and can also form spontancously. Conversion of N5-formyltetrahydrofolate to N5, N10-methenyltetrahy-drofolate, requires ATP, because of an otherwise unfavorable equilibrium. Note that N5-formiminotetrahydrofolate is derived from histidine in a pathway shown in Figure 18-26.

Supplements For Diabetics

Supplements For Diabetics

All you need is a proper diet of fresh fruits and vegetables and get plenty of exercise and you'll be fine. Ever heard those words from your doctor? If that's all heshe recommends then you're missing out an important ingredient for health that he's not telling you. Fact is that you can adhere to the strictest diet, watch everything you eat and get the exercise of amarathon runner and still come down with diabetic complications. Diet, exercise and standard drug treatments simply aren't enough to help keep your diabetes under control.

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