Traube (1858), the active cause of fermentation is due to the action of different enzymes contained in yeast and not to the yeast cell itself.
The preference exhibited by yeast cells for sugar molecules is shared by mould fungi and soluble enzymes in their fermentative actions.
Apiculatus (a common wine yeast) contains neither of these enzymes, and only ferments solutions of glucose or laevulose.
They possess a delicate Laticiferous layer of protoplasm, with numerous small nuclei lining Tissue the walls, while the interior of the tube (corresponding with the cell-vacuole) contains a fluid called latex, consisting of an emulsion of fine granules and drops of very various substances suspended in a watery medium in which various other substances (salts, sugars, rubber-producers, tannins, alkaloids and various enzymes) are dissolved.
The formaldehyde at once undergoes a process of condensation oi- polymerization by the protoplasm of the plastid, while the hydrogen peroxide is said to be decomposed into water and free oxygen by another agency in the cell, of the nature of one of the enzymes of which we shall speak later.
Among the trypsins we have the pa pain of the Papaw fruit (Carica Papaya), the bromelin of the Pine-apple, and the enzymes present in many germinating seeds, in the seedlings of several plants, and in other parts.
Still further insight is afforded by our increasing knowledge of the enzymes, and it is to be remarked that both poisons and enzymes are very common in just such parasitic Fungi as induce discolorations, hypertrophies and the death of cellse.g.
The inability to enter the cells may be due to the lack of chemotactic bodies, to incapacity to form cellulose-dissolving enzymes, to the existence in the hostcells of antagonistic bodies which neutralize or destroy the acids, enzymes or poisons formed by the hyphae, or even to the formation and excretion of bodies which poison the Fungus.
Reference must also be made here to the enzymes or unorganized ferments which occur so largely in the cytoplasm.
Proteolytic Enzymes Catalase .
We may here notice the frequent production of glucose by the action of enzymes upon other carbohydrates.
Fermentation is essentially a chemical process due apparently to the presence of enzymes, developed in the leaf during the earlier curing stages.
Invisible to the microscope, but rendered visible by reagents, are glycogen, Mucor, Ascomycetes, yeast, &c. In addition to these cell-contents we have good indirect evidence of the existence of large series of other bodies, such as proteids, carbohydrates, organic acids, alkaloids, enzymes, &c. These must not be confounded with the numerous substances obtained by chemical analysis of masses of the fungus, as there is often no proof of the manner of occurrence of such bodies, though we may conclude with a good show of probability that some of them also exist preformed in the living cell.
That such enzymes are formed in the protoplasm is evident from the behaviour of hyphae, which have been observed to pierce cell-membranes, the chitinous coats of insects, artificial collodion films and layers of wax, &c. That a fungus can secrete more than one enzyme, according to the materials its hyphae have to attack, has been shown by the extraction of diastase, inulase, trehalase, invertase, maltase, raffinase, malizitase, emulsin, trypsin and lipase from Aspergillus by Bourquelot, and similar events occur in other fungi.
The latter fact, as well as the extraordinary fastidiousness, so to speak, of parasites in their choice of hosts or of organs for attack, point to reactions on the part of the host-plant, as well as capacities on that of the parasite, which may be partly explained in the light of what we 'now know regarding enzymes and chemotropism.
The effect of the abnormal conditions is probably to stop the production of, or weaken or destroy the protective enzymes or antitoxins, the presence of which normally confers immunity on the leaf.
One of the great difficulties in the way of applying this treatment is that in all probability many of the ferments or enzymes are altered during the process of absorption in the same way as the normal ferments of digestion, and unless the tissue enzymes can be isolated and injected subcutaneously the desired results will not be obtained.
Promise of more light on these oxidation fermentations is afforded by the recent discovery that not only bacteria and fungi, but even the living cells of higher plants, contain peculiar enzymes which possess the remarkable property of " carrying " oxygen - much as it is carried in the sulphuric acid chamber - and which have therefore been termed oxydases.
Little is known of the mode of action of bacteria on these plants, but it may be assumed with great confidence that they excrete enzymes and poisons (toxins), which diffuse into the cells and kill them, and that the effects are in principle the same as those of parasitic fungi.
Not only so, the isolation of the cells facilitates the exchange of liquids and gases, the passage in of food materials and out of enzymes and products of metabolism, and thus each unit of protoplasm obtains opportunities of immediate action, the results of which are removed with equal.
Oxydases and Enzymes: Green, The Soluble Ferments and Fermentation (Cambridge, 1899).
We cannot as yet speak definitely with regard to the part played by enzymes in these toxic processes.
Certain toxins resemble enzymes as regards their conditions of precipitation and relative instability, and the fact that in most cases a considerable period intervenes between the time of injection and the occurrence of symptoms has been adduced in support of the view that enzymes are present.
According to this view, then, a part at least of the directly toxic substance is produced in the living body by enzymes present in the so-called toxin obtained from the bacterial culture.
Recent researches go to show that enzymes play a greater part in fermentation by living ferments than was formerly supposed, and by analogy it is likely that they are also concerned in the processes of disease.
Two enzymes called lysozyme and lactoferrin contribute to the antimicrobial and anti-inflammatory characteristics of human milk, which contains more of those beneficial enzymes than animal milk does.