Über alkoholische Gärung ohne Hefezellen

In my last submission to “The Giants’ Shoulders” blog carnival, we saw how the famous surgeon Dr. Joseph Lister deftly demonstrated definitively that fermentation processes were caused by live microbes rather than some sort of mysterious soluble substance that just happened to be associated with microbes. In today’s episode, we will see how Eduard Buchner definitely demonstrated that fermentation was caused by a soluble substance that was associated with microbes, and no microbes are actually needed.

Better still…they’re both right. “Wait…what?” Read on, O Seeker of Microbiological Knowledge, and be enlightened by this month’s entry:

A portrait of Eduard BuchnerBuchner E:”Über alkoholische Gärung ohne Hefezellen”; 1897; Berichte der Deutschen Chemischen Gesellshaft; vol 30, pp 117-124

(That’s “About Alcoholic Fermentation without yeastcells”, published in “Reports [of] the German Chemical Society”, ob Sie kein Deutsch lesen kann.

What Professor Buchner reports here is a delightfully simple exercise in practical biochemistry. He took a batch of yeast cells, which he then completely shredded by grinding them thoroughly in sand. Then he took the resulting goo, wrapped it up in filter paper, and squished the living crap out of it under 400-500 atmospheres of pressure, presumably in some sort of press. I’d like to pause right here to mention that one of the things I really like about going through old scientific papers like this is that the procedures very often turn out to be things one could easily do oneself in one’s own kitchen without resorting to special “scientific” (and expensive) equipment. Anyway…

He found that although he could then filter-sterilize this “juice”, if he added it to sugar-water he would see it start to bubble and produce ethanol, despite the fact that there were no live cells at all in it. He goes on to experiment on this “juice”, and determines that the active principle is probably a proteinaceous substance, that it was soluble in water, and that it was indeed carbon dioxide and ethanol that he could detect being produced when he added sugar. He named the mystery substance “zymase” and went on to win a Nobel Prize in Chemistry for his work a decade later.

Up to the time when Buchner did his work on this, the concept of “vitalism” still had a few supporters left among scientists. “Vitalism”, put simply, is the idea that there is some special, mysterious property of living things that is necessary for performing really complicated chemical changes on carbon compounds. Originally it was assumed that this mysterious property was necessary for any kind of what we still call “organic” chemistry.  By 1897, others had already managed to demonstrate simple “organic” chemical processes without living cells. Buchner’s own paper mentioned invertase (which splits sucrose – a chemical compound of one molecule of glucose bound to one molecule of fructose – into separated glucose and fructose molecules). Apparently Moritz Traub, who Buchner also briefly mentioned in this paper, had also managed to obtain a potato extract that turned one of his lab chemicals blue. And, of course, Friedrich Wöhler had managed to synthesize “organic” urea in a purely chemical manner over half a century before this. The conversion of sugar to ethanol and carbon dioxide is a much more complicated process, and left some room to hypothesize that these kinds of reactions might require some mysterious vital property to perform. Supposedly even Louis Pasteur, himself quite accomplished in fermentation research, held vitalist views. He died only two years before Buchner’s publication demonstrating that even this complicated reaction can be induced without any living things being directly involved at all. Thanks in part to Buchner, “vitalism” in the modern world only exists as “Life Force” newage in bad science fiction and cheesy “Zap-Death Magic and Swordfights” fantasy stories[1].

Interestingly, Buchner was either unaware of Lister’s publication almost two decades previous, or he didn’t entirely believe the results, or perhaps just didn’t believe they applied to alcoholic fermentation by yeasts, because he explicitly hypothesizes that the “zymase” induces fermentation by leaking out of the cells and into the solution around them despite Lister’s demonstration that this was not the case with lactic acid fermentation. As well, nowadays we know that there is no single “zymase” substance but rather several enzymes, each of which catalyses one of the several steps along the way from sugar to ethanol and carbon dioxide. A quick glance at my Biochemistry textbook[2] (Yes, I’m the kind of nerd that keeps his biochemistry textbook long after finishing the class – Dr. Evilia picked a good text) shows 10 different enzymes just to get to pyruvate (11 if you’re starting with sucrose rather than glucose), plus two more to get from pyruvate to ethanol and carbon dioxide. Still, all of these enzymes were in Buchner’s yeast-juice, and Buchner’s experiment is still often credited with being the real beginning of “biochemistry”.  Personally, I’m intrigued to wonder if this easy-to-obtain enzymatic “crude extract” would be of use as a kick-starter in brewing or baking…

The American Society for Microbiology is kind enough to host a translation of this paperhere, so you are encouraged to download a copy and check out the details.

[1] The Vampire crap that seems to have infected popular culture kind of straddles both of these categories. Yes, I said “crap”. The only genre I can think of that I dislike as much as Vampire Crap is Cowboy Crap. I live in constant fear that someone like Joss Whedon will come out with a wildly popular series about cowboy vampires and my head will virtually explode out of sheer disgust…*

[2] Voet D, Voet J: “Biochemistry (3rd Edition)” 2004; John Wiley and Sons; Hoboken NJ

* – Followup: 'The Vampire and the Cowboy'.  I think I'm going to be sick.My Head Asplode!

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The Author is (currently) an autodidactic student of Industrial and Environmental microbiology, who is sick of people assuming all microbiology should be medical in nature, and who would really like to be allowed to go to graduate school one of these days now that he's finished his BS in Microbiology (with a bonus AS in Chemistry). He also enjoys exploring the Big Room (the one with the really high blue ceiling and big light that tracks from one side to the other every day) and looking at its contents from unusual mental angles.

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