{"title":"3-氧戊二酸的非催化和金属离子催化脱羧:一种酶系统模型","authors":"R. Hay, K. N. Leong","doi":"10.1039/J19710003639","DOIUrl":null,"url":null,"abstract":"The uncatalysed decarboxylation of 3-oxoglutaric acid, HO2C·CH2·CO·CH2·CO2H → CH3·CO·CH2·CO2H + CO2 has been studied at 42°. The rate constants for the un-ionised acid, the monoanion, and the dianion are 12 × 10–3 min–1, 45 × 10–3 min–1, and 2·75 × 10–3 min–1 respectively. Because of the higher reactivity of the monoanion, the pH-rate profile for the uncatalysed decarboxylation is bell-shaped with a rate maximum at pH 3·5 (l= 0·1M). The enhanced reactivity of the monoanion appears to be due to intramolecular hydrogen bonding between the carbonyl group and the un-ionised carboxy-group. The practical ionisation constants of 3-oxoglutaric acid are pK1= 3·23 and pK2= 4·27 at 0·01M. The decarboxylation of 3-oxoglutaric acid, unlike that of acetoacetic acid, is catalysed by transition-metal ions, so that in the presence of metal ions there is a rapid loss of one molecular equivalent of carbon dioxide followed by a slower loss of a second molecular equivalent in the uncatalysed reaction. The catalytic effects of copper(II), nickel(II), and manganese(II) have been studied in some detail. It has been found that 2,2′-bipyridyl which is capable of π-bonding with the metal ions enhances the catalytic activity of manganese(II) by a factor of 10 while the effect with copper(II) and nickel(II) is less marked (ca. 2 times). The possible significance of these effects in the action of the metal-activated decarboxylases is discussed, as manganese(II) is the biologically important metal ion in the enzymatic reactions.","PeriodicalId":17321,"journal":{"name":"Journal of The Chemical Society A: Inorganic, Physical, Theoretical","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"12","resultStr":"{\"title\":\"The uncatalysed and metal-ion catalysed decarboxylation of 3-oxoglutaric acid: a model for an enzyme system\",\"authors\":\"R. Hay, K. N. Leong\",\"doi\":\"10.1039/J19710003639\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The uncatalysed decarboxylation of 3-oxoglutaric acid, HO2C·CH2·CO·CH2·CO2H → CH3·CO·CH2·CO2H + CO2 has been studied at 42°. The rate constants for the un-ionised acid, the monoanion, and the dianion are 12 × 10–3 min–1, 45 × 10–3 min–1, and 2·75 × 10–3 min–1 respectively. Because of the higher reactivity of the monoanion, the pH-rate profile for the uncatalysed decarboxylation is bell-shaped with a rate maximum at pH 3·5 (l= 0·1M). The enhanced reactivity of the monoanion appears to be due to intramolecular hydrogen bonding between the carbonyl group and the un-ionised carboxy-group. The practical ionisation constants of 3-oxoglutaric acid are pK1= 3·23 and pK2= 4·27 at 0·01M. The decarboxylation of 3-oxoglutaric acid, unlike that of acetoacetic acid, is catalysed by transition-metal ions, so that in the presence of metal ions there is a rapid loss of one molecular equivalent of carbon dioxide followed by a slower loss of a second molecular equivalent in the uncatalysed reaction. The catalytic effects of copper(II), nickel(II), and manganese(II) have been studied in some detail. It has been found that 2,2′-bipyridyl which is capable of π-bonding with the metal ions enhances the catalytic activity of manganese(II) by a factor of 10 while the effect with copper(II) and nickel(II) is less marked (ca. 2 times). The possible significance of these effects in the action of the metal-activated decarboxylases is discussed, as manganese(II) is the biologically important metal ion in the enzymatic reactions.\",\"PeriodicalId\":17321,\"journal\":{\"name\":\"Journal of The Chemical Society A: Inorganic, Physical, Theoretical\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":0.0000,\"publicationDate\":\"1971-01-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"12\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Journal of The Chemical Society A: Inorganic, Physical, Theoretical\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/10.1039/J19710003639\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of The Chemical Society A: Inorganic, Physical, Theoretical","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1039/J19710003639","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
The uncatalysed and metal-ion catalysed decarboxylation of 3-oxoglutaric acid: a model for an enzyme system
The uncatalysed decarboxylation of 3-oxoglutaric acid, HO2C·CH2·CO·CH2·CO2H → CH3·CO·CH2·CO2H + CO2 has been studied at 42°. The rate constants for the un-ionised acid, the monoanion, and the dianion are 12 × 10–3 min–1, 45 × 10–3 min–1, and 2·75 × 10–3 min–1 respectively. Because of the higher reactivity of the monoanion, the pH-rate profile for the uncatalysed decarboxylation is bell-shaped with a rate maximum at pH 3·5 (l= 0·1M). The enhanced reactivity of the monoanion appears to be due to intramolecular hydrogen bonding between the carbonyl group and the un-ionised carboxy-group. The practical ionisation constants of 3-oxoglutaric acid are pK1= 3·23 and pK2= 4·27 at 0·01M. The decarboxylation of 3-oxoglutaric acid, unlike that of acetoacetic acid, is catalysed by transition-metal ions, so that in the presence of metal ions there is a rapid loss of one molecular equivalent of carbon dioxide followed by a slower loss of a second molecular equivalent in the uncatalysed reaction. The catalytic effects of copper(II), nickel(II), and manganese(II) have been studied in some detail. It has been found that 2,2′-bipyridyl which is capable of π-bonding with the metal ions enhances the catalytic activity of manganese(II) by a factor of 10 while the effect with copper(II) and nickel(II) is less marked (ca. 2 times). The possible significance of these effects in the action of the metal-activated decarboxylases is discussed, as manganese(II) is the biologically important metal ion in the enzymatic reactions.