人類細(xì)胞中的所有生物反應(yīng)都依賴于酶的作用,，它們作為催化劑促使生物反應(yīng)在幾毫秒內(nèi)發(fā)生,。那么,，如果不存在酶將會怎樣？美國科學(xué)家近日研究稱,，在沒有酶作用的情況下,，某種生物反應(yīng)的自然發(fā)生需要23億年，相當(dāng)于地球年齡的一半,。研究論文發(fā)表于11月11日的美國《國家科學(xué)院院刊》（PNAS）,。
研究人員稱，這一反應(yīng)對于血色素和葉綠素的生物合成必不可少,，當(dāng)沒有酶存在時,，它的半衰期是23億年；當(dāng)用酶尿卟啉原脫羧酶催化時,，反應(yīng)速度驚人地增加,，只需幾毫秒就能發(fā)生。酶存在與否造成的差別堪比細(xì)菌細(xì)胞直徑和地球與太陽之間距離的差距,。
論文通訊作者,、美國北卡羅萊納大學(xué)的Richard Wolfenden說：“這個酶對于地球上的植物和動物必不可少。我們所研究的是進(jìn)化不得不克服的難題,，而酶跨越了這一巨大的障礙——半衰期為23億年的反應(yīng),。”
了解生物反應(yīng)所需的時間在多個方面具有重要的意義。它能幫助科學(xué)家將酶與人工催化劑進(jìn)行比較,，同時,，觀測非常緩慢的生物反應(yīng)也能得到有助于藥物研發(fā)的重要信息。Wolfenden說：“行使重要催化作用的酶很容易成為藥物研發(fā)最靈敏的標(biāo)靶,。我們研究的酶非常迷人,，因為它們的催化能力是空前的,。”（生物谷Bioon.com）
生物谷推薦原始出處：
PNAS,，vol. 105 no. 45 17328-17333，Charles A. Lewis, Jr.,，Richard Wolfenden
Uroporphyrinogen decarboxylation as a benchmark for the catalytic proficiency of enzymes
Charles A. Lewis, Jr. and Richard Wolfenden
The magnitude of an enzyme's affinity for the altered substrate in the transition state exceeds its affinity for the substrate in the ground state by a factor matching the rate enhancement that the enzyme produces. Particularly remarkable are those enzymes that act as simple protein catalysts, without the assistance of metals or other cofactors. To determine the extent to which one such enzyme, human uroporphyrinogen decarboxylase, enhances the rate of substrate decarboxylation, we examined the rate of spontaneous decarboxylation of pyrrolyl-3-acetate. Extrapolation of first-order rate constants measured at elevated temperatures indicates that this reaction proceeds with a half-life of 2.3 × 109 years at 25 °C in the absence of enzyme. This enzyme shows no significant homology with orotidine 5′-monophosphate decarboxylase (ODCase), another cofactorless enzyme that catalyzes a very slow reaction. It is proposed that, in both cases, a protonated basic residue (Arg-37 in the case of human UroD; Lys-93 in the case of yeast ODCase) furnishes a counterion that helps the scissile carboxylate group of the substrate leave water and enter a relatively nonpolar environment, stabilizes the incipient carbanion generated by the departure of CO2, and supplies the proton that takes its place.
