Take the 2-minute tour ×
Biology Stack Exchange is a question and answer site for biology researchers, academics, and students. It's 100% free, no registration required.

Do invertebrates (like Drosophila and C.elegans) have a urea cycle?

share|improve this question
add comment

2 Answers

up vote 1 down vote accepted

C. elegans is missing all of the urea cycle enzymes. Drosophila is missing just one enzyme, but there's a shortcut which may enable it to nonetheless complete the cycle. (For comparison, here's the pathway map for human with the complete cycle.)

share|improve this answer
add comment

Perhaps worth adding that the role of the urea cycle in terrestrial vertebrates is the disposal of excess N derived from protein metabolism. Such animals are ureotelic. Arthropods, in contrast, are uricotelic, using uric acid for N disposal, so it would make no sense for them to have a functional urea cycle. (Nematodes - I don't know.)

The importance of avoiding having a urea cycle when it is not needed is illustrated by the situation in yeast (Saccharomyces cerevisiae). In yeast some of the enzymes that would be part of the urea cycle are used in degrading arginine, while others are used in the biosynthesis of arginine. Yeast cells will carry out one or the other of these processes depending upon their metabolic status. If both processes were to be active at the same time this would result in a urea cycle that would waste ATP. This is avoided by having a multienzyme complex consisting of arginase and ornithine transcarbamoylase (in the degradative and biosynthetic pathways respectively), allowing reciprocal regulation so that only one of these is active at any time.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.