They are phenylalanine, valine, threonine, tryptophan, methionine, leucine, isoleucine, lysine, and histidine. Some amino acids, such as cysteine and methionine contain sulfur. It inhibits the conversion of the sulfur amino acid methionine to cysteine. Aspartate can be converted into lysine, asparagine, methionine and threonine. Whereas cysteine, homocysteine, methionine and ethionine possess the thiol equivalents. Instead, recommended intakes are identified for the sulfur-containing amino acids methionine and cysteine. It is also relatively low in the sulfur-containing amino acids methionine and cysteine. The latter is a component of the amino acids cysteine and methionine. It contains no tryptophan and is deficient in isoleucine, threonine, and methionine. It is used to label the sulfur-containing amino-acids methionine and cysteine. These enzymes play a key role in the biosynthesis of lysine, threonine, and methionine. Methyl-B converts homocysteine, in a reaction catalyzed by homocysteine methyltransferase, to methionine. Sulfides are important in biology, notably in the amino acid methionine and the cofactor biotin. Many legumes, however, are deficient in the essential amino acid methionine, which grains contain. Hence treatment includes both betaine and a diet low in methionine.