Hood J M, Fowler A V, Zabin I
Proc Natl Acad Sci U S A. 1978 Jan;75(1):113-6. doi: 10.1073/pnas.75.1.113.
The amino acid sequence of beta-galactosidase (beta-D-galactoside galactohydrolase, EC 3.2.1.23) has been compared to itself and to other proteins. Two segments, each of about 380 amino acids, comprising the first three-fourths of the polypeptide chain, were found to be very similar to each other. It is concluded that they are homologous. The carboxyl-terminal fourth has a high percentage of amino acid identities with dihydrofolate reductase of Escherichia coli, suggesting these sequences also are homologous. A model for the origin of beta-galactosidase is presented. The overall similarity of beta-galactosidase to lac repressor does not appear to be significant.
已将β-半乳糖苷酶（β-D-半乳糖苷半乳糖水解酶，EC 3.2.1.23）的氨基酸序列与其自身以及其他蛋白质进行了比较。发现该多肽链前三分之二由两个各约含380个氨基酸的片段组成，它们彼此非常相似。由此得出结论，它们是同源的。羧基末端的四分之一与大肠杆菌二氢叶酸还原酶具有较高的氨基酸同一性百分比，表明这些序列也是同源的。本文提出了一个β-半乳糖苷酶起源的模型。β-半乳糖苷酶与乳糖阻遏物的总体相似性似乎并不显著。
