We are having a hard time understanding the question, and the answer that we fou

Question

We are having a hard time understanding the question, and the answer that we found in Chegg matches the answer in the textbook, which is also not helpful. PLEASE HELP!

ATCase underwent reaction with tetranitromethane to form a colored nitrotyrosine group (Wavelength max = 430 nm) in each of its catalytic chains. The absorption by this reporter group depends on its immediate environment. An essential lysine residue at each catalytic site also was modified to block the binding of substrate. Catalytic trimers from this doubly modified enzyme were then combined with native trimers to form a hybrid enzyme. The absorption by the nitrotyrosine group was measured on addition of the substrate analog succinate. What is the significance of the alteration in the absorbance at 430 nm?

Explanation / Answer

This experiment explains allosteric regulation of enzymes. ATCase is an allosteric enzyme with catalytic and regulatory units fused together to form a complete enzyme. Thus, any modification to the catalytic chains would impair the proper functioning of the enzyme. This impairment would be visible in the form of an alteration in the alteration of absorbance. If there is no enzyme activity (which is most likely since the catalytic site has been chemically modified) their would be no change in the absorbance. However, if there is enzyme activity there will be an alteration in the absorbance as the chemical group (colored nitrotyrosine group) is not affecting the enzyme function.

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