The pyruvate dehydrogenase (pdh) complex catalyzes the oxidative decarboxylation of pyruvate to acetyl-coa and co, multiple copies of pyruvate dehydrogenase (e1), dihydrolipoyl transacetylase (e2), and dihydrolipoyl dehydrogenase (e3) along with five cofactors form the pdh complex. biochemists have studied the pdh complex for decades, in part due to its interesting use of substrate channeling during catalysis.
what is the benefit of substrate channeling?

a. the pdh active site forms in the hydrophobic core of the complex instead of a surface-exposed region.
b. reaction progress is not limited by the diffusion constant.
c. intermediates of a multistep reaction sequence do not dissociate from the enzyme complex.
d. the pdh complex sequesters excess substrate to use at later time.
e. every intermediate or product made by the pdh complex enters the citric acid cycle as a substrate.

americans began to notice growing differences between the northern and southern sections of the country. there were more people living in cities in the north, which made it more urban. more people lived on farms in the south, which made it more rural. while many people were farmers in the northern states, there were now other ways to make a living, such as working in mechanical cotton gins factories manufacturing cloth, tools and other goods. people in the north supported high tariffs on goods imported from europe because the extra cost encouraged people to “buy american” instead. in the southern states, planters did not like tariffs because they sold most of their production to europe and bought their tools from there as well. southerners believed the protective tariff was something that only northern factory owners keep their profits high. so the southern politicians came up with an idea. they would opt out. they would simply ignore the protective tariff. it was ‘null and void’ in south carolina. the state would not collect the taxes on goods imported into south carolina, no matter what the president said they had to do. this decision led to the nullification crisis.