A 10-year-old child is evaluated for developmental delays, n…

A 10-year-old child is evaluated for developmental delays, nearsightedness, and recurrent blood clots. Laboratory testing reveals markedly elevated homocysteine levels in blood and urine. The physician suspects a form of homocystinuria caused by impaired conversion of homocysteine to downstream sulfur-containing metabolites. Which vitamin is most likely to improve symptoms in some forms of this disorder?

A researcher develops a mouse in which glutamine synthetase…

A researcher develops a mouse in which glutamine synthetase is selectively eliminated from the perivenous region of the liver acinus. The periportal region remains completely normal, including normal expression of CPS-I and all urea cycle enzymes. After a protein-rich meal, blood leaving the liver is found to contain elevated ammonia concentrations despite normal periportal urea cycle activity. Which function of the liver acinus has been disrupted most directly?