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NEWSLETTER 8 - Extension 2 : Saccharides in Our Biochemistry
(Updated September 2005)
Diet
Biochemistry
Enzymes
Health and Research
Conclusion
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Saccharides in Our Diet
Our modern diet provides mainly the polysaccharides saccharose,
maltose and lactose. They contain the monosaccharides glucose, fructose,
and galactose, only three of the eight monosaccharides our biochemistry
uses (Table 1).
| Common Name |
Polysaccharide |
Formed of |
and of |
| Sugar, Sucrose |
Saccharose |
Glucose |
Fructose |
| Starch |
Maltose |
Glucose |
Glucose |
| Milk Sugar |
Lactose |
Glucose |
Galactose |
Table 1: Composition of the three main polysaccharides occurring in
our diet.
Human diets have changed over time and not always for the better.
Hunter-gatherer societies ate a variety of foods including roots,
wild grains, berries, leaves and nuts. After the advent of agriculture,
people settled down to regular consumption of a more limited variety
of easy-to-grow foods, such as potatoes wheat and rice.
Archeologists tell us that the earliest hunter-gatherers people were actually taller, healthier, and had
better teeth and bone structure than the agricultural people that came later.
More recently, modern refining methods further diminished the variety of nutritional components consumed
in conventional diets. Whole wheat was replaced by refined flour, whole wild rice by polished rice and
whole potatoes by mashed potato flakes.
Most of the source for the saccharides needed by our cells were lost by these changes. Science is only
scarcely beginning to understand the consequent effect on our health.
(Bill McAnalley. The Potential Significance of Dietary Sugars in Management of Osteoarthritis and
Rheumatoid Arthritis: A Review. Proceedings of the Fisher Institute for Medical Research.
Vol.1, N°1, November 1997. 6-10)
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Saccharides in Plant and Human Biochemistry
Plant biochemistry synthesizes mono- and polysaccharides from carbonic acid and water.
Human biochemistry synthesizes glucose from lactate and from pyruvate. Human biochemistry is able (in perfect
health condition) to convert the two or three saccharides occurring in modern diet into seven of the eight
saccharides and saccharide derivatives it needs to assume all of its functions. Synthesis and conversion
occurs with the assistance of vitamins from the B group and with minerals, as magnesium, manganese, selenium,
iron, and zinc acting as enzyme activators.
The eight saccharides and saccharide derivatives the human biochemistry
uses are : Glucose, Galactose, Mannose, Fucose, Neuraminic
N-acetyl acid (NeuNAc), N-acetyl Glucosamine, N-acetyl Galactosamine,
and Xylose.
Human biochemistry uses these eight saccharides in cell and organ
structure, in cell communication, and in immunity.
Saccharides in Cell and in Organ Structure
Saccharides participate in cell and organ structure in association with proteins. Saccharides account for 5%
of the mass of a cell membrane. The most frequent saccharide in cell and organ structure is
N-acetyl glucosamine, followed by N-acetyl galactosamine.
N-acetyl glucosamine and N-acetyl galactosamine -- absent in our diet -- have to be synthesized from the
saccharides provided in the diet. The synthesis of these two saccharides starting from glucosamine and
galactosamine -- if these saccharides are available in the diet -- is
much less expensive for our biochemistry than their synthesis from glucose.
Saccharides in Cell Communication
Cells communicate with "messages" they carry on the surface of their membrane. The
"messages" are glycoforms, molecules formed essentially of saccharides. Glycoforms protrude from
the external surface of the cell membrane. Glycoforms contain the monosaccharides mannose, N-acetyl
galactosamine, and galactose.
Saccharides in Immunity
The immunity of a cell depends on the "messages" expressed by the glycoforms on the surface of its
membrane. If in a message, words are missing or misspelled -- if some saccharide is missing in the
glycoform-- the message is erroneous with all the
consequences of it.
An error in the message disguises the real identity of the cell bearing it. An error in the message can
bring other cells "reading& it to act as if the bearer of the error was a foreign body.
Many diseases have in common the inability of certain cells to send correct messages -- to synthesize the
correct glycoforms.
This inability may result from an error in the genetic code that governs the synthesis of the
glycoforms.
The inability may also result from the absence of the needed saccharide in the diet or from a combination of
the two conditions.
The Carbohydrate Deficient Glycoprotein Syndrome
results from a mannose deficiency.
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The Role of Enzymes in Our Saccharide Biochemistry
The conversion from one molecule of saccharide into another is an enzymatic process involving multiple
intermediary steps.
As an example, the conversion from glucose to mannose-6-phosphate involves three such intermediary steps
(Table 2).
| From |
Enzyme |
Direction |
To |
| Glucose |
Phosphate-6-kinase |
reversible |
Glucose-6-phosphate |
| Glucose-6-phosphate |
Isomerase |
reversible |
Fructose-6-phosphate |
| Fructose-6-phosphate |
Isomerase |
reversible |
Mannose-6-phosphate |
Table 2: The conversion of glucose to mannose-6-phosphate involves
three enzymatic steps. The process is theoretically reversible.
The conversion from glucose to galactose involves six intermediary
enzymatic steps (Table 3). The process is reversible, galactose
can be converted to glucose.
| From |
Enzyme |
Direction |
To |
| Glucose |
Phosphate-6-kinase |
reversible |
Glucose-6-phosphate |
| Glucose-6-phosphate |
Mutase |
reversible |
Glucose-1-phosphate |
| Glucose-1-phosphate |
Pyrophosphorylase |
reversible |
UDP-Glucose |
| UDP-Glucose |
4 -Epimerase |
reversible |
UDP-Galactose |
| UDP-Galactose |
Uridyl-Transferase |
reversible |
Galactose-1-phosphate |
| Galactose-1-phosphate |
Phosphate-6-kinase |
reversible |
Galactose |
Table 3: The conversion of galactose to glucose involves six
enzymatic steps. (UDP stands for: Uridine DiPhosphate). The process is reversible, galactose can be
converted to glucose.
The conversion from glucose to
Glucosamine-Acetyl-1-Phosphate involves eight intermediary enzymatic steps (Table 4).
| From |
Enzyme |
Direction |
To |
| Glucose |
Phosphate-6-kinase |
reversible |
Glucose-6-phosphate |
| Glucose-6-phosphate |
Isomerase |
reversible |
Fructose-6-phosphate |
| Fructose-6-phosphate |
Amidotransferase |
reversible |
Glucosamine-1-Phosphate |
| Glucosamine-1-Phosphate |
Acetyl-CoA-transferase |
reversible |
Glucosamine-Acetyl-6-Phosphate |
| Glucosamine-Acetyl-6-Phosphate |
Mutase |
reversible |
Glucosamine-Acetyl-1-Phosphate |
| Glucosamine-Acetyl-1-Phosphate |
Pyrophosphorylase |
reversible |
UDP-Glucosamine-Acetyl |
| UDP-Glucosamine-Acetyl |
Pyrophosphorylase |
reversible |
Glucosamine-Acetyl-1-Phosphate |
Table 4: The conversion of glucose to Glucosamine-Acetyl-1-
Phosphate involves eight enzymatic steps. (UDP stands for: Uridine DiPhosphate).
The same Glucosamine-Acetyl-1-Phosphate is obtainable from glucosamine in a much more economical
way involving only two enzymatic steps (Table 5).
| Glucosamine |
Acetyl-CoA-transferase |
reversible |
Glucosamine-Acetyl |
| Glucosamine-Acetyl |
Phosphokinase |
reversible |
Glucosamine-Acetyl-1-Phosphate |
Table 5: The conversion of glucosamine to
Glucosamine-Acetyl-1-Phosphate involves two enzymatic steps.
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