The Fall of Vitalism. Enzymes

Yet if life forms could perform chemical feats that could not be performed in inanimate nature, these had to be accomplished by some material means (unless one were willing to depend on the supernatural, which nineteenth-century scientists were not willing to do). The nature of the material means slowly came into view.

Even in the eighteenth century, chemists had observed that a reaction could sometimes be hastened by the introduction of a substance that did not, to all appearances, take part in the reaction. Observations of this sort accumulated and attracted serious attention in the early nineteenth century.

A Russian chemist, Gottlieb Sigismund Kirchhoff (1764-1833), showed in 1812 that if starch were boiled with dilute acid, the starch broke down to a simple sugar, glucose. This would not happen if the acid were absent and yet the acid did not seem to take part in the reaction, for none of it was used up in the breakdown process.

Four years later, the English chemist, Humphry Davy (1778-1829), found that platinum wires encouraged the combination, at ordinary temperatures, of various organic vapors, such as alcohol, with oxygen. The platinum certainly did not seem involved in the reaction.

These and other examples came to the attention of Berzelius who wrote on the subject in 1836 and who suggested the name "catalysis" for the phenomenon. This is from Greek words meaning "to break down" and possibly refers to the acid-catalyzed breakdown of starch.

Ordinarily, alcohol burns in oxygen only after being heated to a high temperature at which its vapors ignite. In the presence of the platinum catalyst, however, the same reaction takes place without preliminary heating. It could therefore be argued that the chemical processes in living tissue proceed, as they do, under very gentle conditions, because certain catalysts are present in tissue that are not present in the inanimate world.

Indeed, in 1833, shortly before Berzelius dealt with the subject, the French chemist, Anselme Payen (1795-1871), had extracted a substance from sprouting barley which could break down starch to sugar even more readily than acid could. He named it "diastase." Diastase and other similar substances were named "ferments" because the conversion of starch to sugar is one of the preliminaries in the fermentation of grain.

Ferments were soon obtained from animal organisms as well. The first of these was from digestive juice. Reaumur had shown that digestion was a chemical process, and in 1824, the English physician, William Prout (1785-1850), had isolated hydrochloric acid from stomach juices. Hydrochloric acid was a strictly inorganic substance and this was a surprise to chemists generally. However, in 1835, Schwann, one of the founders of the cell theory, obtained an extract from stomach juice that was not hydrochloric acid but which decomposed meat even more efficiently than the acid did. This, which Schwann named "pepsin" (from a Greek word meaning "to digest") was the true ferment.

More and more ferments were discovered and it became quite apparent in the latter half of the nineteenth century that these were the catalysts peculiar to living tissue; the catalysts that made it possible for organisms to do what chemists could not. Proteins remained the vitalist shield for there were many reasons for believing that these ferments were protein in nature (though this was not definitely demonstrated until the twentieth century).

It was a strain on the vitalist position, however, that some ferments worked as well outside the cell as inside. The ferments isolated from digestive juices performed their digestive work very well in a test tube. One might suspect that if one could obtain samples of all the various ferments, then any reaction that went on in a living organism could be duplicated in the test tube and without the intervention of life, since the ferments themselves (at least, those studied) were indubitably nonliving. What's more, the ferments followed the same rules obeyed by inorganic catalysts, such as acids or platinum.

The vitalist position, then, was that ferments from digestive juices did their work outside the cells anyway. A digestive juice poured into the intestines might as well be poured into a test tube. The ferments that remained within the cell and did their work only within the cell were a different matter. Those, insisted the vitalists, were beyond the grip of the chemist.

Ferments came to be divided into two classes: "unorganized ferments" or those that worked outside cells, like pepsin; "organized ferments" or those that worked inside cells only, like those that enabled yeast to convert sugar into alcohol.

In 1876, the German physiologist, Wilhelm Kiihne (1837-1900), suggested that the word, ferment, be reserved for those processes requiring life. Those ferments which could work outside cells, he suggested be called "enzymes" (from Greek words meaning "in yeast"), because they resembled the ferments in yeast in their action.

Then, in 1897, the whole vitalist position was, in this respect, unexpectedly exploded by the German chemist, Eduard Buchner (1860-1917). He ground yeast cells with sand until not one was left intact and then filtered the ground-up material, obtaining a cell-free quantity of yeast juice. It was his expectation that this juice would have none of the fermenting ability of living yeast cells. It was important, however, that the juice be kept from contamination with microorganisms or it would then contain living cells after all and the test would not be a good one.

One time-tested method of preserving materials against contamination by microorganisms is the addition of a concentrated sugar solution. Buchner added this and found, to his amazement, that the sugar began to undergo a slow fermentation, although the mixture was absolutely nonliving. He experimented further, killing yeast cells with alcohol and finding that the dead cells would ferment sugar as readily as the live ones would.

As the nineteenth century drew to a close, it was recognized that all ferments, organized as well as unorganized, were dead substances that might be isolated from cells and made to do their work in the test tube. The name "enzyme" was applied to all ferments alike and it was therefore accepted that the cell contained no chemicals that could work only in the presence of some life force.

Pasteur's dictum that without life there could be no fermentation was found to apply only to situations as they occurred in nature. The interfering hand of man could so treat the yeast cell that though the cell and its life was destroyed, the constituent enzymes remained intact and then fermentation could be made to proceed without life.

This was the most serious defeat vitalism had yet endured but, in a sense, the vitalist position was far from shattered. Much remained to be discovered about the protein molecule (both enzymes and nonenzymes), and it could not be considered certain that the life force would not, at some point or other, make itself evident. In particular, Pasteur's (and Virchow's) other dictum that no cell could arise except from a pre-existing cell remained and, while that remained, there was still something special about life that perhaps the hand of mere man might not touch.

However, the heart went out of the vitalist position. Individual biologists might still speak diluted forms of vitalism in theory (and some do even today) but none seriously act upon it. It is generally accepted that life follows the laws that govern the inanimate world; that there is no problem in biology that is innately beyond solution in the laboratory, nor any life process that may not be imitated there in the absence of life. The mechanistic view is supreme.