Note to users. If you're seeing this message, it means that your browser cannot find this page's style/presentation instructions -- or possibly that you are using a browser that does not support current Web standards. Find out more about why this message is appearing, and what you can do to make your experience of our site the best it can be.

Science 25 February 2005:
Vol. 307. no. 5713, p. 1165
DOI: 10.1126/science.307.5713.1165o
Prev | Table of Contents | Next

This Week in Science

Rigorous tests of hypotheses about adaptation must identify those mutations responsible for changes in function and show that they are selectively advantageous under particular conditions. Zhu et al. (p. 1279, published online 13 January 2005) reconstruct the selective basis of an adaptive event that occurred at the dawn of the eukaryotes billions of years ago, focusing on two variants of isocitrate dehydrogenase (IDH) that have different cofactor preferences, either nicotinamide adenine dinucleotide, NAD, or its phosphate, NADP. Genetic engineering techniques were used to create an ancestral version of an enzyme. Subsequent selection experiments showed why the cofactor specificity of the enzyme changed. NADP is linked to use of acetate as a substrate, and the appearance of the derived NADP-IDH from the ancestral NAD-IDH reflects the type of substrate used to generate adenosine triphosphate and reducing power. By eliminating other sources of reduced NADPH, selection acts against the NAD-dependent phenotype. Thus, growth on acetate favored the evolution of an NADPH isocitrate dehydrogenase.




To Advertise     Find Products

Science. ISSN 0036-8075 (print), 1095-9203 (online)