Decreased MeCbl alongside normal cobalamin uptake is suggestive of decreased intracellular methionine biosynthesis. Remethylation of homocysteine to methionine by MTR requires the derivative of cobalamin, methylcobalamin. Methionine synthase eventually becomes inactive due to the oxidation of its cobalamin cofactor. The progression of neurological manifestations of cobalamin deficiency is generally gradual. This reaction requires cobalamin as a cofactor. It inactivates the cobalamin form of vitamin B by oxidation. This process uses N5-methyl tetrahydrofolate as the methyl donor and cobalamin (vitamin B)-related enzymes. The latter is the first macrocyclic intermediate common to haem, chlorophyll, sirohaem and cobalamin itself. The substance was a cobalamin, which the discoverers named vitamin B. Cobinamide is the final compound in the biosynthesis of cobalamin. Salvage pathways also exist for ceramide, cobalamin, cell wall components, and tetrahydrobiopterin in various organisms. Cleavage of this complex produces free cobalamin, translocating from lysosome to cytoplasm. Transcobalamins are carrier proteins which bind cobalamin (B). The MMACHC gene product and cobalamin reductases enable the interconversion of cyano- and alkylcobalamins. SNAC is able to form a noncovalent complex with cobalamin while preserving its chemical integrity.