Cofactors in Mutated Enzymes

Gene mutations in vitamin metabolisms

There are gene mutations that impact the metabolism of vitamins. These mutations can lead to reduced enzyme function in the metabolism of the vitamins. They are rather common.

The MTHFR mutation reduces the conversion of 5,10-Methylene-THF to 5-Methyl-THF in the folate metabolism. This reaction is an important step in the methylation cycle and the mutation can lead to low levels of 5-MTHF, high levels of homocysteine and low S-adenosylmethionine production.

MTHFR reaction:
5,10-Methylene-THF +NADPH–> 5-Methyl-THF + NADP+ H+(cofactor: FAD)

Other gene mutations may impact vitamin metabolisms, like mutations in the MTR and MTRR gene that may interfere with methylcobalamin metabolism. Vitamin D receptor mutations are associated with a lower number of vitamin D receptors, reducing the effect of vitamin D in the body. Beta-carotene 15,15′-dioxygenase is an enzyme in the vitamin A metabolism and mutations might impact retinol levels.

Beta-carotene 15,15′-dioxygenase (BCO): beta-Carotene + O2–> 2retinal (cofactor: iron as Fe2+)

 

Influence of Cofactors

A mutation in the MTHFR gene can lead to a decreased function of the MTHFR enzyme, reducing levels of 5-MTHF. The reduced levels of 5MTHF can cause low S-adenosylmethionine production and high homocysteine levels

Cofactors for MTHFR are FAD and NADPH. Deficiencies in cofactors can impact the enzyme function.

A study showed correlation of the homocysteine levels and the riboflavin status in people with a MTHFR 677C>T polymorphism (1). Also, in people with a homozygous mutation riboflavin, supplementation could overall reduce homocysteine levels by 22%, up to 40% in people with lower riboflavin status (2).

This shows, that the presence of cofactors can determine the activity of the mutated enzyme.

It seems that sufficient riboflavin status may actually be more important for people with a MTHFR mutation, than  without. There were findings that a mutated MTHFR enzyme has less affinity for its cofactor, which makes it especially sensitive to lower riboflavin status. The mutated enzyme is more likely to lose/dissociate from its flavin cofactor, which was found to be ‘slowed in the presence of methyltetrahydrofolate or adenosylmethionine'(3). Adenosylmethionine is a natural inhibitor of MTHFR activity, so even though it stabilizes the binding to the cofactor it might reduce the enzymes activity.

A study on MTHFR and MTRR mutations also found a connection between enzyme activity and cofactor presence. They discovered that the function of enzymes with a MTHFR 677C>T polymorphism depended on riboflavin status and that the activity of methionine synthase reductase in MTRR mutations reacted to cobalamin/riboflavin and cobalamin status (4).

 

These studies highlight how cofactor levels are important in the function of mutated MTHFR and MTRR enzymes. Many people with ME/CFS that have these mutations start on the ‘methylation-protocol’, with high-dose methylfolate and methylcobalamin supplementation. In many cases, there is an initial improvement that doesn’t last or that is followed by negative side-effects.

Since mutated enzymes are more sensitive to the presence of cofactors, it might be important to have a stronger focus on enough riboflavin and cobalamin intake, especially in people with homozygous mutations. Otherwhise there could be a chance that high-dose methylation supplements further deplete these cofactors and thereby reduce other processes where cobalamin or riboflavin are required. Cobalamin might include other forms of vitamin B12, apart from methylcobalamin.

 

More information on supplements in ‘My Experience->supplements’

Posts on other gene mutations

 

References:

  1. https://www.ncbi.nlm.nih.gov/books/NBK6145/“MTHFR may be sensitive to riboflavin status,11 particularly in subjects with the 677C→T substitution of the MTHFR gene. In subjects with the TT genotype, higher riboflavin intake could be necessary for the formation of adequate amounts of 5-methyl-THF involved in homocysteine remethylation.”“Plasma tHcy was 1.4 µmol/l higher in the lowest compared to the highest riboflavin quartile in a multiple regression model adjusted for folate and other determinants of tHcy. The riboflavin-tHcy relationship was modified by the MTHFR 677C→T polymorphism and was essentially confined to subjects with the T allele (Fig. 2). The riboflavin-tHcy relationship was not significantly modified by levels of serum folate……Jacques et al studied 450 subjects from the Framingham Offspring cohort, selected according to the MTHFR 677C→T polymorphism and equally distributed between the CC, CT and TT genotypes.23 They found an inverse association between plasma concentrations of riboflavin and plasma tHcy, but only in subjects with the TT genotype and plasma folate below the median (12.5 nmol/l).”
  2. https://www.ncbi.nlm.nih.gov/pubmed/16380544
    “Here, we report for the first time significant lowering of homocysteine in response to riboflavin supplementation in individuals homozygous for the MTHFR 677C→T polymorphism, with levels decreasing by as much as 22% overall and markedly so (by 40%) in those with lower riboflavin status at baseline.”
  3. http://www.pnas.org/content/98/26/14853.abstract?ijkey=eecfef7c289a34ac5e164c3e040e35cd70f594c7&keytype2=tf_ipsecsha
  4. https://www.ncbi.nlm.nih.gov/m/pubmed/25322900/
    “The effect of the MTHFR 677C>T polymorphism on tHcy depends on riboflavin status, that of the MTRR 66A>G polymorphism on cobalamin and riboflavin status and that of the MTRR 524C>T polymorphism on cobalamin status.”