Watt K W, Maruyama T, Riggs A
J Biol Chem. 1980 Apr 25;255(8):3294-301.
The amino acid sequence of the beta chain of component III of the hemoglobin of the tadpole of the bullfrog. Rana catesbeiana, has been determined. Comparison of this sequence with the 117 identified residues of the beta chain in the adult bullfrog shows that 50% (59 of 117) of the residues are identical; 55% (81 of 146) are identical in the comparison with the human beta chain. Tadpole hemoglobin lacks most of the residues believed responsible for the alkaline Bohr effect in human hemoglobin: the NH2 terminus is acetylated and histidine H5 (alpha 122) in the human alpha chain is replaced by glutamine in the tadpole. Although the tadpole beta chain has a COOH-terminal histidine, the hydrogen bond responsible in human hemoglobin for about one-half the normal alkaline Bohr effect cannot form, because asparagine rather than aspartate is present at position 94. However, histidyl residue H21 (beta 143), invoked to explain the reversed "acid" Bohr effect in human hemoglobin, is present in the tadpole chain and is adjacent to a seryl residue (beta 144) rather than lysyl residue, so that the pK of the beta 143 histidine should be higher than in human hemoglobin. This could explain the substantial acid Bohr effect in tadpole hemoglobin.
牛蛙（牛蛙属）蝌蚪血红蛋白组分III的β链氨基酸序列已被确定。将该序列与成年牛蛙β链中117个已鉴定的残基进行比较，结果表明50%（117个中的59个）的残基是相同的；与人类β链比较时，55%（146个中的81个）是相同的。蝌蚪血红蛋白缺乏大部分被认为是人类血红蛋白中碱性玻尔效应原因的残基：氨基末端被乙酰化，人类α链中的组氨酸H5（α122）在蝌蚪中被谷氨酰胺取代。虽然蝌蚪β链有一个羧基末端组氨酸，但人类血红蛋白中约一半正常碱性玻尔效应所涉及的氢键无法形成，因为94位存在的是天冬酰胺而非天冬氨酸。然而，用于解释人类血红蛋白中反向“酸性”玻尔效应的组氨酸残基H21（β143）存在于蝌蚪链中，并且与一个丝氨酸残基（β144）相邻而非赖氨酸残基，因此β143组氨酸的pK值应高于人类血红蛋白中的pK值。这可以解释蝌蚪血红蛋白中显著的酸性玻尔效应。
