Which amino acid is not taken up well by liver, and must be supplied by its essential amino acid precursor?

Question

Quizplus · Accepted Answer

Cysteine is the amino acid that is not taken up well by the liver and must be supplied by its essential amino acid precursor, methionine. This is because cysteine has a sulfhydryl group (-SH) which is oxidized to form disulfide bonds (-S-S-) in proteins. The liver does not have as high of a demand for disulfide bonds as other tissues, so it cannot efficiently uptake cysteine. Therefore, methionine is converted to cysteine via the transsulfuration pathway in other tissues like the kidneys and pancreas, and cysteine is then transported to the liver for further metabolism.

Which Amino Acid Is Not Taken Up Well by Liver