Ayala F J, Barrio E, Kwiatowski J
Department of Ecology and Evolutionary Biology, University of California, Irvine 92697, USA.
Proc Natl Acad Sci U S A. 1996 Oct 15;93(21):11729-34. doi: 10.1073/pnas.93.21.11729.
We have investigated the evolution of glycerol-3-phosphate dehydrogenase (Gpdh). The rate of amino acid replacements is 1 x 10(-10)/site/year when Drosophila species are compared. The rate is 2.7 times greater when Drosophila and Chymomyza species are compared; and about 5 times greater when any of those species are compared with the medfly Ceratitis capitata. This rate of 5 x 10(-10)/site/year is also the rate observed in comparisons between mammals, or between different animal phyla, or between the three multicellular kingdoms. We have also studied the evolution of Cu,Zn superoxide dismutase (Sod). The rate of amino acid replacements is about 17 x 10(-10)/site/year when comparisons are made between dipterans or between mammals, but only 5 x 10(-10) when animal phyla are compared, and only 3 x 10(-10) when the multicellular kingdoms are compared. The apparent decrease by about a factor of 5 in the rate of SOD evolution as the divergence between species increases can be consistent with the molecular clock hypothesis by assuming the covarion hypothesis (namely, that the number of amino acids that can change is constant, but the set of such amino acids changes from time to time and from lineage to lineage). However, we know of no model consistent with the molecular clock hypothesis that would account for the increase in the rate of GPDH evolution as the divergence between species increases.
我们研究了3-磷酸甘油脱氢酶（Gpdh）的进化情况。当比较果蝇物种时，氨基酸替换率为1×10⁻¹⁰/位点/年。当比较果蝇和食酪蝇物种时，该速率高出2.7倍；当将这些物种中的任何一个与地中海实蝇（Ceratitis capitata）比较时，速率高出约5倍。这个5×10⁻¹⁰/位点/年的速率也是在哺乳动物之间、不同动物门之间或三个多细胞界之间比较时观察到的速率。我们还研究了铜锌超氧化物歧化酶（Sod）的进化情况。当在双翅目昆虫之间或哺乳动物之间进行比较时，氨基酸替换率约为17×10⁻¹⁰/位点/年，但在比较动物门时仅为5×10⁻¹⁰，在比较多细胞界时仅为3×10⁻¹⁰。随着物种间差异增加，SOD进化速率明显下降约5倍，这可以通过假设共变假说（即能够发生变化的氨基酸数量是恒定的，但这类氨基酸的集合会随时间和谱系而变化）与分子钟假说相一致。然而，我们不知道有任何与分子钟假说一致的模型能够解释随着物种间差异增加GPDH进化速率的增加。
