Forsman C, Jonsson B H, Lindskog S
Biochim Biophys Acta. 1983 Oct 28;748(2):300-7. doi: 10.1016/0167-4838(83)90307-2.
The 250 MHz 1H-NMR spectrum of horse carbonic anhydrase I (or B) (carbonate hydro-lyase, EC 4.2.1.1) was measured as a function of pH under various conditions. Eight resonances corresponding to histidine C-2 protons and four resonances corresponding to histidine C-4 protons were identified and assigned to individual histidine residues in the enzyme molecule. Substantial similarities between horse and human carbonic anhydrases I were demonstrated. While the human enzyme has three titratable histidine residues in its active site, the horse enzyme has only two, His-67 in the human enzyme being replaced by Gln in the horse enzyme (Jabusch, J.R., Bray, R.P. and Deutsch, H.F. (1980) J. Biol. Chem. 255, 9196-9204). This substitution has small but significant effects on the behaviour of the other active-site histidines. His-64 and His-200. However, His-64 has an anomalously low pKa value also in horse isoenzyme I, as previously observed in human isoenzyme I (Campbell, I.D., Lindskog, S. and White, A.I. (1974) J. Mol. Biol. 90, 469-489).
在各种条件下，测定了马碳酸酐酶I（或B）（碳酸水解酶，EC 4.2.1.1）在250 MHz下的1H-NMR谱随pH的变化情况。确定了对应于组氨酸C-2质子的8个共振峰和对应于组氨酸C-4质子的4个共振峰，并将它们分配给酶分子中的各个组氨酸残基。结果表明马和人碳酸酐酶I之间存在显著相似性。人碳酸酐酶在其活性位点有3个可滴定的组氨酸残基，而马碳酸酐酶只有2个，人碳酸酐酶中的His-67在马碳酸酐酶中被Gln取代（Jabusch，J.R.，Bray，R.P.和Deutsch，H.F.（1980）J. Biol. Chem. 255，9196 - 9204）。这种取代对其他活性位点组氨酸His-64和His-200的行为有微小但显著的影响。然而，正如之前在人同工酶I中观察到的那样，His-64在马同工酶I中的pKa值也异常低（Campbell，I.D.，Lindskog，S.和White，A.I.（1974）J. Mol. Biol. 90，469 - 489）。
