Chemical structure of Vitamin B12
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Cyanocobalamin

The name vitamin B12 (or B12 for short) is used in two different ways. In a broader sense it refers to a group of Co-containing compounds known as cobalamins - cyanocobalamin (an artifact formed as a result of the use of cyanide in the purification procedures), hydroxocobalamin and the two coenzyme forms of B12, methylcobalamin (MeB12) and 5-deoxyadenosylcobalamin (adenosylcobalamin - AdoB12). more...

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In a more specific way, the term B12 is used to refer to only one of these forms, cyanocobalamin, which is the principal B12 form used for foods and in nutritional supplements.

Pseudo-B12 refers to B12-like substances which are found in certain organisms, such as Spirulina spp. (blue-green algae, cyanobacteria). However, these substances do not have B12 biological activity for humans.

Structure

B12 is the most chemically complex of all the vitamins. B12's structure is based on a corrin ring, which, although similar to the porphyrin ring found in heme, chlorophyll, and cytochrome, has two of the pyrrole rings directly bonded. The central metal ion is Co (cobalt). Four of the six coordinations are provided by the corrin ring nitrogens, and a fifth by a dimethylbenzimidazole group. The sixth coordination partner varies, being a cyano group (-CN), a hydroxyl group (-OH), a methyl group (-CH₃) or a 5'-deoxyadenosyl group (here the C5' atom of the deoxyribose forms the covalent bond with Co), respectively, to yield the four B12 forms mentioned above. The covalent C-Co bond is the only carbon-metal bond known in biology.

Synthesis

B12 cannot be made by plants or by animals, as the only type of organisms that have the enzymes required for the synthesis of B12 are bacteria and archaea.

Functions

Coenzyme B12's reactive C-Co bond participates in two types of enzyme-catalyzed reactions.

  1. Rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents, an oxygen atom of an alcochol, or an amine.
  2. Methyl (-CH₃) group transfers between two molecules.

In humans there are only two coenzyme B12-dependent enzymes:

  1. MUT which uses the AdoB12 form and reaction type 1 to catalyze a carbon skeleton rearrangement (the X group is -COSCoA). MUT's reaction converts MMl-CoA to Su-CoA, an important step in the extraction of energy from proteins and fats (for more see MUT's reaction mechanism)
  2. MTR, a methyl transfer enzyme, which uses the MeB12 and reaction type 2 to catalyzes the conversion of the amino acid Hcy into Met (for more see MTR's reaction mechanism).

Read more at Wikipedia.org


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The link between adrenal fatigue and DNA methylation
From Townsend Letter for Doctors and Patients, 5/1/05 by Susan Solomon

Editor:

Adrenal function is vital to life: without cortisol we die. This fact has been known since the 1930s when it was described by Banting and Best. Glucocorticoids are essential for maintaining carbohydrate, protein and fat metabolism. They also have a permissive effect which allows for glucagon and catecholamines to work. Important glucocorticoid effects include the normal functioning of the nervous system, water metabolism, vascular reactivity, regulation of circulating lymphocytes and the immune system and "resistance to stress." Complete lack of adrenal function is a disease state known as Addison's Disease. Conventional medicine only recognizes two states: you either make cortisol or you don't. Allopathic physicians are unaware of the decline in adrenal function as illness becomes chronic.

The etiology of adrenal fatigue begins with a "stressor," or in functional medicine terms, a "trigger." Triggers fall into several categories: psychosocial stress, environmental toxins (radon, mercury, mold), infectious organisms (fungal, bacterial, parasitic), food allergies (wheat, corn, sugar, milk), and other toxins (alcohol, drugs, prescription medications) to name a few. In addition, stressful events such as surgery or car accidents place a huge (usually unrecognized) load on the adrenal glands. The initial response to each of the above events is to elevate cortisol levels to help cope with the stress. However, over time, the adrenals become weakened and lose their circadian rhythm. This is due in large part to poor nutrition. All stressful events require increased amounts of several nutrients: vitamin C, pantothenic acid, B6 (pyridoxine), B12 (methylcobalamin), and folate. Interestingly, if the adrenal glands are catheterized and a "stressor" is introduced, the first chemical to leave the adrenals is not cortisol as one would suspect, but large amounts of vitamin C. These nutrients are severely lacking in the typical American diet or are not found in high enough amounts. More often than not "orthomolecular" dosing is necessary to correct the deficits.

The initial response to any stress is the hypersecretion of cortisol, but over time (approximately one year) there develops a negative feedback and a genuine "fatigue" causing reduced levels of DHEA-S and cortisol. The end result is an organism with reduced immunity, increased likelihood of autoimmune disease, heart attacks, elevated cholesterol and triglycerides, skin disorders, carbohydrate cravings, protein wasting, fatigue and depression (to name but a few). Physicians normally view these as separate events in a given organ and do not see that the symptoms represent a disease process (inflammation) that may occur in one or more organs simultaneously. Therefore everyone with any chronic disease, not just cardiovascular disease, should be screened using DHEA-S and a homocysteine level. As DHEA-S decreases, the level of homocysteine rises, with a concomitant decrease in most B-vitamins, but especially folate and B12. The currently accepted norms for these parameters are too permissive, reminiscent of glucose control in years past. All of our organs are linked and nothing that happens is random. We are all the result of our genetic interaction with our environment.

With the establishment of "disease" another pivotal biochemical event happens: abnormal methyl metabolism. Multiple reports in the recent literature link abnormal DNA methylation with the onset of cancer in laboratory animals. Undoubtedly this occurs in humans as well.

It is my clinical experience that as soon as a patient's DHEA-S falls to below 160 the ability to make methyl groups nosedives as well. These patients may then present with symptoms of depression (inability to synthesize S-adenosylmethionine), joint pain (inability to make methylsulfonylmethionine), and gastric acid reflux disease (inability to make betaine or trimethylglycine), to name a few. Not only does the ability to make methyl groups decrease, but the ability to convert to a methylated product is also compromised. For example, in chronically ill individuals the use of B12--as either the cyanocobalamin or the hydroxocobalamin form seems to do little to improve fatigue or mental functioning. The ideal compound to replenish B12 is methylcobalamin--the only active form. In each case, oral supplementation with the missing methyl-containing substrate ameliorates the symptoms. In each of the scenarios listed, the severity of the illness correlates with the level of the reduced or deficient DHEA-S and the concomitant elevated homocysteine level. The elevated homocysteine level is not only a marker for inflammation, but it is a marker for deficient B vitamins as well. The stage is now set for abnormal DNA methylation and the induction of cancer.

Efforts to repair adrenal fatigue include nutrients (in their most active form), glandular preparations, DHEA (and in severe cases cortisol itself), and lifestyle modifications with removal of triggers. Even with these measures, expect adrenal recovery to take 3 to 5 years.

Bibliography

Shealy, CN. Chronic Pain Management. TLfDP. 258:22-23, January 2005

Ganong. WF. Review of Physiology. McGrawh-Hill. 1999: pages 344-362

Poirer, LA. The effects of diet, genetics and chemicals on toxicity and aberrant DNA methylation: an introduction. J Nutr 2002 Aug: 132 (8 Suppi): 2336S-2339S

Shames, RL. Nutritional Management of Stress-Induced Dysfunction. ANSR-Applied Nutritional Science Reports. 2002

www.Dr.Lam.com: Adrenal Fatigue

Miller, AL. The Methionine-Homocysteine Cycle and Its Effects on Cognitive Diseases Alternative Medicine Review. Vol 8, number 1, page 7-13.

Susan Solomon, MD

12201 Gayton Road Suite 201

Richmond, Virginia 23238 USA

COPYRIGHT 2005 The Townsend Letter Group
COPYRIGHT 2005 Gale Group

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