finally i found some papers and rich´s explanations and if feel he is right and fredd is wrong. just my opinion though.
you have got to love rich´s calm way of explaining things , making difficult to read studies understandable to lay people :
Protection of aquo/hydroxocobalamin from reduced glutathione by a B12 trafficking chaperone
We identified a bovine B(12) trafficking chaperone bCblC in Bos taurus that showed 88% amino acid sequence identity with a human homologue. The protein bCblC was purified from E. coli by over-expression of the encoding gene. bCblC bound cyanocobalamin (CNCbl), methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl) in the base-off states and eliminated the upper axial ligands forming aquo/hydroxocobalamin (OH(2)/OHCbl) under aerobic conditions. A transition of OH(2)/OHCbl was induced upon binding to bCblC. Interestingly, bCblC-bound OH(2)/OHCbl did not react with reduced glutathione (GSH), while the reaction of free OH(2)/OHCbl with GSH resulted in the formation of glutathionylcobalamin (GSCbl) and glutathione disulfide (GSSG). Furthermore we found that bCblC eliminates the GSH ligand of GSCbl forming OH(2)/ OHCbl. The results demonstrated that bCblC is a B(12) trafficking chaperone that binds cobalamins and protects OH(2)/OHCbl from GSH, which could be oxidized to GSSG by free OH(2)/OHCbl.
rich v k:
Hi, ukme.
Thank you for posting this. Here's what I believe it is saying:
The study involves one of the intracellular (inside the cells) vitamin B12 processing proteins, taken from the cow. It is called the CblC in the human, but is called bCblC in the cow, with the b standing for bovine. This protein serves as a trafficking chaperone. That means that it protects and conveys cobalamin (B12) between steps in the intracellular processing pathways that start with various forms of B12 received by the cell, and end with it being converted to the two active coenzyme forms, methylcobalamin and adenosylcobalamin. It is necessary to protect B12 during this process, because it is very chemically reactive, and will react with toxins and be lost if it is not protected and channeled within the proper biochemical pathways.
The authors report that the bovine version of this protein is similar to that of the human in its amino acid sequence, differing by only 12% of its amino acids.
The authors produced a large enough quantity of the pure bCblC by using E. coli bacteria to make it, by grafting the gene for the cow's protein into the bacteria DNA, and then separating the bCblC protein out after it was produced by the bacteria. They then studied it in vitro, i.e. isolated in the laboratory, rather than in the living cells of the cow. This is done because it is a much simpler chemical system, in which individual reactions can be isolated and observed.
By adding different forms of B12 to a solution containing bCblC, they found that this chaperone would bind all of them under aerobic conditions (that is, in contact with the atmosphere). (Note that the interiors of cells in the body are under less oxiziding conditions than was this solution exposed to the air, so this needs to be considered when oxidation/reduction reactions are involved, and presumably the authors did consider this.) When bCblC bound any of these B12 forms (cyanocobalain, mmethylcobalamin, or adenosylcobalamin), it removed the upper axial ligand (cyano-, methyl-, or adenosyl-) and converted them all to aquocobalamin (this is the same as hydroxocobalamin, because aquocobalamin exists in equilibrium with its dissociated or ionized state, which is hydroxocobalamin, at the pH of the cells). When these forms of B12 are bound to bCblC, they are bound in the base-off configuration. That means that the ligand that is on the other ("bottom") side of the B12 molecule shifts into a different configuration, but is still attached to the molecule.
While the B12 (cobalamin) was bound to bCblC, it would not react with glutathione. That is, it was protected from reacting (i.e. "chaperoned.") However, free (unbound) hydroxocobalamin will react with glutathione to form glutathionylcobalamin and glutathione disulfide (oxidized glutathione). This means that the aquo-/hydroxo-cobalamin is chemically reduced by glutathione and is then bound to another glutathione molecule. Glutathione disulfide is the oxidized form of glutathione. When glutathione chemically reduces another molecule, it becomes oxidized in doing so. Oxidation and reduction go hand-in-hand in chemistry, because they involve transfer of an electron from one species to another. The one that gives up the electron is oxidized, and the one that receives it is reduced. "Chemically reduced" in this case means that the cobalt ion in the cobalamin molecule is given an electron, which reduces its oxidation state. This ion can have three different oxidation states, i.e. +1, +2, and +3. When it is reduced, it is much more chemically reactive, that is to being oxidized by other species.
They also found that bCblC will react with glutathionylcobalamin, removing the glutathionyl ligand and converting it to bound aquo-/hydroxo-cobalamin.
They conclude that bCblC is a trafficking chaperone that binds cobalamins (this was already known) and that it also prevents aquo/hydroxo-cobalamin from reacting with glutathione, which it will do in its free state.
The complete intracellular B12 processing pathways have not been worked out in detail yet, but it is known that the CblC protein plays an important intermediate role. This protein enables the cell normally to use the whole variety of forms of B12. It first removes whatever ligand is attached to the molecule, and then, using other proteins (enzymes), it normally re-forms as much methylcobalamin and adenosylcobalamin as it needs.
Some people inherit mutations in the CblC protein's gene, and this causes them not to be able to carry out this normal pathway. Freddd may be a person who has such a mutation, since he has reported that his body is not able to use cyanocobalamin, hydroxocobalamin or glutathionylcobalamin to make the active coenzyme forms of B12 effectively, so he must give his cells the active forms directly. Apparently he must give them in large dosages directly into the blood by sublingual application or injection so that enough will diffuse across the cell membranes to supply what his cells need.
The exact position of glutathione in the intracellular B12 processing pathways has not been completely worked out. It is known that glutathione will protect B12 from reactions with foreign substances, and this work shows that glutathione will chemically reduce B12. Perhaps glutathione is able to rescue B12 that has become oxidized, and then feed it to CblC so that it can be chaperoned to the next step in the pathway. This is still an area of ongoing research. I'm very interested in this, because the GD-MCB hypothesis that I have proposed holds that glutathione normally protects B12, so that when it becomes depleted, B12 is lost from its normal intracellular processing pathways, and this shuts down the methylation cycle and brings about the onset of ME/CFS. As far as I can tell, the results of this paper would not contradict the hypothesis, but I need to get a complete copy of the paper and study it more carefully, because abstracts can sometimes be misleading or leave out a lot.
Best regards,
Rich
rich v k:
Thank you. I read the full paper, and also took another look at an earlier paper that was referenced in it, from Ruma Banerjee's group:
http://www.jbc.org/content/284/48/33418.long
As a result, I think I will modify my GD-MCB hypothesis for the pathogenesis of ME/CFS a little. In the past, I have suggested that glutathione protects B12 at an intermediate stage of its processing inside the cells. It appears from the Banerjee paper that it also plays a role in helping the CblC protein to remove the ligands from methyl B12 and adenosyl B12 so that they can be reformed later in the amounts needed by the cell. Without enough glutathione, it seems to me that this part of the B12 pathway would be blocked. Therefore, glutathione depletion would still lead to a functional B12 deficiency and a partial block in the methylation cycle.
The paper you cited seems to imply by its title that the interaction of glutathione with B12 is something to be avoided. That is normally not the case, and in fact, it is very important that glutathione be present for proper B12 metabolism. In Freddd's case, he has found glutathione to be detrimental. I think the reason is probably that his CblC protein is mutated, such that it is not able to retrieve cobalamin from glutathionylcobalamin, as this protein is normally able to do, shown by this paper.
Best regards,
Rich