Methionine is one of the sulfur containing amino acids and is important for many bodily functions. It acts as a lipotropic agent to prevent excess fat buildup in the liver and the body, is helpful in relieving or preventing fatigue and may be useful in some cases of allergy because it reduces histamine release. Patients with a sulfa allergy should not take this injection.
Methionine synthase (MTR) is a methyltransferase enzyme, which uses the MeB12 and reaction type 2 to catalyze the conversion of the amino acid (Hcy) back into methionine (Met). This functionality is lost in vitamin B12 deficiency, and can be measured clinically as an increased homocysteine level in vitro. Increased homocysteine can also be caused by a folic acid deficiency, since B12 helps to regenerate the tetrahydrofolate (THF) active form of folic acid. Without B12, folate is trapped as 5-methyl-folate, from which THF cannot be recovered unless a MTR process reacts with the 5-methyl-folate with homocysteine to produce methionine and THF, thus decreasing the need for fresh sources of THF from the diet. The THF may be produced in the conversion of homocysteine to methionine, or may be obtained in the diet. It is converted by a non-B12-dependent process to 5,10-methylene-THF, which is involved in the synthesis of thymine. Reduced availability of 5,10-methylene-THF results in problems with DNA synthesis, and ultimately in ineffective production cells with rapid turnover, in particular blood cells, and also intestinal wall cells which are responsible for absorption.
Vitamin B12-dependent MTR reactions may also have neurological effects, through an indirect mechanism. Adequate methionine (with, folate like, must otherwise be obtained in the diet, if it is not regenerated from homocysteine by a B12 dependent reaction) is needed to make S-adenosyl-methionine (SAMe), which is in turn necessary for methylation of myelin sheath phospholipids. Although production of SAMe is not B12 dependent, help in recycling for provision of one adequate substrate for it (the essential amino acid methionine) is assisted by B12. In addition, SAMe is involved in the manufacture of certain neurotransmitters and catecholamines in brain metabolism. These neurotransmitters are important for maintaining mood, possibly explaining the reason for depression is associated with B12 deficiency. Methylation of the myelin sheath phospholipids may also depend on adequate folate, which in turn is dependent on MTR recycling, unless ingested in relatively high amounts.
Methionine combined with choline highly helpful to break down fats in the body and prevents fat build ups in the liver which helps to weight loss and control the body weight.
