Methylene tetrahydrofolate reductase (MTHFR) is the rate-limiting enzyme in the methyl cycle, and it is encoded by the MTHFR gene. Methylenetetrahydrofolate reductase catalyzes the conversion of 5,10-methylenetetrahydrofolate to 5-methyltetrahydrofolate, a cosubstrate for homocysteine remethylation to methionine.he enzyme is coded by the gene with the symbol MTHFR on chromosome 1 location p36.3 in humans. There are DNA sequence variants (genetic polymorphisms) associated with this gene. In 2000 a report brought the number of polymorphisms up to 24.
In this article, the city populations listed are those of metro areas, not necessarily city proper populations within the bounds of city limits. Mexico City is identified as the most populous city in North America, with a population of 21,339,771. This is the second largest metropolitan area in the world, and the population continues to grow, at an annual rate of 1.8%. Mexico City has taken it place as not only the largest city in North America, but as the economic engine of the Mexican nation as well.
M exicoâs ten largest cities (2009 population) are: 1  Mexico City 19,982,000 (Metropolitan Area). 2  Guadalajara 4,365,000. 3  Monterrey 3,986,000. 4  Puebla 2,647,000. 5  Tijuana 1,784,000.