Methionine, on the other hand, is needed in the diet because while it can be degraded to and then regenerated from homocysteine, it cannot be synthesized de novo.
De novo pathways of nucleotides do not use free bases: adenine (abbreviated as A), guanine (G), cytosine (C), thymine (T), or uracil (U).
But in conditions of obesity, insulin resistance, or type 2 diabetes de novo lipogenesis is reduced in adipose tissue (where carbohydrate-responsive element-binding protein (ChREBP) is the major transcription factor) and is increased in the liver (where sterol regulatory element-binding protein 1 (SREBP-1c) is the major transcription factor).
[7] Obesity and high-fat diets cause levels of carbohydrate-responsive element-binding protein in adipose tissue to be reduced.
[9] De novo fatty-acid synthesis is regulated by two important enzymes, namely acetyl-CoA carboxylase and fatty acid synthase.
De novo fatty-acid synthesis is mainly not active in human cells, since diet is the major source for it.