Hey Guys I was wondering if you could me with this question. I\'ve already gotte
ID: 34186 • Letter: H
Question
Hey Guys I was wondering if you could me with this question. I've already gotten it wrong twice and I was so sure about my answer.
- It can't be A because transketolases don't use Schiff base, only transaldolases.
- B seemed right to me but it's not the only correct answer
- C Also seemed right (I tried it with B)
- D is wrong because only transaldolase does that
- and E can't be right because the transketolast isn't used for that anyway. Ribulose-5-phosphate isomerase and epimerase does this.
Any thoughts? Thanks!!
Which of the following statements about transketolases that operate in the non-oxidative phase of the pentose phosphate pathway are correct? Transketolases use a covalent catalytic mechanism that involves the formation of a Schiff base between the enzyme and the substrate. Transketlases always use a ketose to donate a 2-carbon moiety to an aldose acceptor Atanskeidlse catalyreseroacion sdohegphuose 7 The transketolase mechanism involves a nucleophilic attack by a carbanion on a carbonyl-containing aldehyde group. A t phosphate+ glyceraldehyde-3-phosphate->fructose-6-phosphate + erythrose-4-phosphate Transketolase inhibition would block the non-oxidative formation of xylose-5- phosphate and ribose-5-phosphate starting from glycolytic intermediates.Explanation / Answer
D is the correct answer.It is because
Transketolase is an enzyme of both the pentose phosphate pathway in all organisms and the Calvin cycle of photosynthesis. It catalyzes two important reactions, which operate in opposite directions in these two pathways. In the first reaction of the non-oxidative pentose phosphate pathway, the cofactor thiamine diphosphate accepts a 2-carbon fragment from a 5-carbon ketose (D-xylulose-5-P), then transfers this fragment to a 5-carbon aldose (D-ribose-5-P) to form a 7-carbon ketose (sedoheptulose-7-P).