Glycogen

“ We know that one of the principal functions of the liver is to maintain at a constant level the quantity of glucose held by the blood, by means of the reserves of glycogen secreted by the hepatic cells. Now, in this circulation of glucose and accumulation of glycogen, it is easy to see that the effect is as if the whole effort of the organism were directed towards providing with potential energy the elements of both the muscular and the nervous tissues. ”

“ A necessary preliminary of the fermentation of glycogen is its conversion by a diastatic enzyme into a fermentable sugar, and it is probable that the effect of the disorganisation of the cell by toluene is that this enzyme finds more ready access to the glycogen, which is stored in the plasma of the cell. No such acceleration of autofermentation is effected by the addition of toluene to yeast-juice, and hence the result is not due to an acceleration of the action of the diastatic enzyme on the glycogen. ”

“ The starchy portion is converted, through the digestive ferments in the saliva, pancreatic, and intestinal juices, into dextrin and grape sugar; absorbed through the intestines, it is deposited in the form of glycogen in the liver, the muscles also absorbing a large part of this glycogen. Through work this glycogen is exhausted. Thus work is performed mainly at the expense of the carbohydrates, which are the prime generators of muscular energy. We have also seen that the above-mentioned Japanese coolies perform their incredible muscular efforts largely on such food only. ”

“ Figure 19.—Carl F. Cori (b. 1896) and his wife, Gerty T. Cori (1896-1957) received part of the Nobel Prize in Medicine and Physiology in 1947 for their study on glycogen conversion. In the course of this study, they identified glucose 1-phosphate, now usually referred to as “Cori ester,” and its function in the glycogen cycle. (Photo courtesy National Library of Medicine, Washington, D.C.)
[Pg 197] The study of this function is the newest phase in the history of phosphorus and represents the culmination of the previous efforts. ”

“ It passes, not into the bile, but into the hepatic veins, and the general circulation, where it serves in its decomposition to generate heat, and probably to hasten cell growth. In the vegetable and animal world, in the germinating seed, and in cartilage, muscle and epidermis of the fœtus and in the amnios, glycogen and glucose are found in abundance. The liver, too, the great center for the production of glycogen, is relatively much larger in the young and growing animal, and also in the adult animal which has great power of assimilation. ”

“ Should food substances, such as sugar, increase in the blood beyond a low per cent, they are converted into a form, like glycogen, in which they are held in reserve, or, for the time being, placed beyond the reach of the cells. When, however, the supply is reduced, the stored-up materials reënter the blood and again become available to the cells. ”

“ The chief use of glucose, and of other forms of digested carbohydrates is in the formation of heat and energy. Glucose is oxidized chiefly in the muscles, producing carbon dioxid, water, and some lactic acid. Another function of glucose in the blood is to build up or form fat. Fat is a form of stored food which is not so readily available for use as are glycogen and glucose. ”

“ Very few other kinds of edible flesh contain as much as one percent of glycogen. Glycogen is a transitory product which tends naturally to be broken up into other substances, and, hence, even in horse meat after slaughter, it may rapidly disappear and thus, unless the meat is examined at once, very little glycogen may be found in it. ”

“ The conditions under which the experiment must be carried out are not very favourable to the attainment of extreme accuracy. Yeast-juice contains glycogen and a diastatic enzyme which converts this into dextrins and finally into sugar. This process goes on throughout fermentation, tending to increase the sugar present and to make the apparent loss of sugar less than the sum of the products. ”

“ But large quantities of sugar in the blood are certainly inimical to the well-being of the organism, and we find in the liver a tendency for the sugar to undergo a transformation, i. e., a retrogression into glycogen, either through simple dehydration or otherwise. Further, with reference to the possible conversion of proteoses into peptone by the substance of the intestine, we have a perfectly analogous case in the behavior of the intestinal mucous membrane toward maltose, the final product of amylolytic action. ”

“ Acetic Acid Fuchsin. A few drops of fuchsin are added to a 2 per cent solution of acetic acid. With this solution the nuclei are not only brought out more sharply but they are stained red.
7. Lugol’s Solution. Dilute Lugol’s solution to a pale yellow color. It brings out the contours of cell and nucleus, and has a specific reaction with glycogen and amyloid, giving both a brown color. Since glycogen is dissolved out in water-solutions tests for glycogen in fresh tissues should be made with iodine-glycerin or iodine-gum (Lugol’s one part, gum arabic 100 parts) . ”

“ There is that which until recent years was supposed to be the sole hepatic process—the formation of bile. In some liver-cells are masses of oil-globules, which seem to imply a carbo-hydrate metamorphosis. And then, of leading importance, comes the extensive production of that animal-starch known as glycogen—a substance which, in each of the cells generating it, is contained in a plexus of protoplasmic threads: again a nitrogenous body diffused through a mass which is now formed out of sugar and is now dissolved again into sugar. ”

“ Glucose (often called also dextrose, fruit sugar, or grape sugar) occurs widely distributed in plants, most commonly in the juices of ripening fruits, where it is usually associated with fructose and sucrose, the two hexoses being easily derived from sucrose by hydrolysis. Glucose is also produced by the hydrolysis of many of the more complex carbohydrates, by the action either of enzymes or of dilute acids; lactose, maltose, raffinose, starch, and cellulose, as well as many glucosides all yielding glucose as one of the products of their hydrolysis. ”

“ First, that fats as such may be translocated from cell to cell, since cell-walls and cell protoplasm seem to be permeable to oil if it is a sufficiently fine emulsion; or they may be hydrolyzed into glycerol and fatty acids and translocated from cell to cell in these forms and recombined into fats in the new location. Second, that fats are formed from glucose in some plants, from sucrose and from starch in others, and from mannite and similar compounds in still other species. ”

“ Other species of plants always show considerable quantities of simple sugars in the vegetative tissues, and some even store up their reserve carbohydrate food material in the form of glucose or sucrose. Attempts have been made to associate the type of carbohydrate formed in cell synthesis with the botanical families to which the plants belong, but with no very great success. For each individual species, however, the form of carbohydrate produced is always the same, at least under normal conditions of growth. ”

“ All natural glucosides are hydrolyzed into a sugar and another organic residue by boiling with mineral acids; although they vary widely in the ease with which this hydrolysis is brought about.
In most cases, the glucoside is easily hydrolyzed by an enzyme which occurs in the same plant tissue, but in different cells than those which contain the glucoside. Injury to the tissues, germination processes, and perhaps other physiological activities of the cells, result in bringing the enzyme in contact with the glucoside and the hydrolysis of the latter takes place. ”

“ The starch of the bran or flour is first transformed into glucoses and dextrin by the action of an unorganized ferment called cerealin. The glucoses are then fermented by certain species of bacteria, Bacillus furfuris being perhaps the chief, with the formation of lactic, acetic, formic and butyric acids, and the evolution of carbon dioxide, hydrogen, nitrogen, and a small quantity of sulphuretted hydrogen.
The principal acid produced is lactic; the acetic acid is produced directly from the glucoses by the above-mentioned bacteria without any preliminary alcoholic fermentation by yeasts. ”

“ Normally, glucose is oxidized in the body to its final oxidation products, carbon dioxide and water. But when many difficultly oxidizable substances, such as chloral, camphor, turpentine oil, aniline, etc., are introduced into the body, the organism has the power of combining these with glucose to form glucosides. These so-called "paired" compounds are then oxidized to the corresponding glucuronic acid derivatives and eliminated from the body in the urine. No phenomenon similar to this occurs in plants, however, and glucuronic acid has never been found in plant tissues. ”

“ The polysaccharides, which are generally insoluble, must be broken down into the simpler soluble sugars before they can be translocated to other organs of the plant for immediate, or future, use. When they reach the storage organs, they may be recondensed into insoluble polysaccharides, or stored as soluble sugars. Examples of the latter type of storage are, sucrose in beet roots, glucose in onion bulbs, etc. Sometimes, this habit of storage seems to be a species characteristic; as potatoes store starch, while beets, growing in the same soil and under exactly the same environment, store sugar. ”

“ As the oxygen and hydrogen in sugar are in the proportion by volume of one of oxygen to two of hydrogen, as in water, sugar is said to be a carbo-hydrate; or, as one might phrase it, it is hydrated carbon. Suppose, as 1 now do, we pour some strong sulphuric acid, which has a great affinity for water, upon a bit of lump sugar, you see the lump soon becomes a black mass of carbon or charcoal. This group of carbo-hydrates includes the various kinds of sugars, starches, and gums. Carbo-hydrates are always present in a diet. ”

“ Test: Add yeast to the urine and keep at 15° to 20° C. when if glucose is present, it becomes cloudy and gives off carbon dioxide, or add a little caustic potash solution, and a few drops of cupric sulphate solution until it is blue: then heat and a red precipitate of cupreous oxide is thrown down. The amount gives the ratio of glucose. Uric acid, hypoxanthin or mucus causes brown precipitate in the absence of glucose: peptone, creatin, creatinine, pepsine and urinary pigment prevent its formation though glucose be present. ”

“ The same cells of the plant that make sugar have the power to make protein, using as raw materials some of the sugar along with the substances brought in with the soil water. The energy for the manufacture of protein comes from the oxidation of some of the sugar or starch in the leaf. The finished protein has about the same energy value, weight for weight, as has the starch from which it was mainly derived.
When an animal eats a plant or part of one, he is eating for the sake of the sugar or sugar products which the plant has made. ”

“ In addition to the pancreatic juice and bile there is a secretion known as intestinal juice which is poured out by small glands scattered along the wall of the small intestine. These secrete enzymes which convert the various kinds of sugar into the particular sugar, glucose, which is the one the body can use. The glands also secrete an enzyme which can carry on to completion protein digestion. Thus there is ample insurance that all the foodstuffs shall be made ready for the use of the body. ”

“ Tube, and sterilise as for bouillon.
Ordinary commercial glucose serves the purpose equally well, but is not recommended, as during the process of sterilisation it causes the medium to gradually deepen in colour.
Note.—In certain cases a corresponding percentage of lactose, maltose, or saccharose is substituted for glucose.
Sugar Gelatine.—
1. Prepare nutrient gelatine (vide page 164, sections 1 to 7) . Measure out 1000 c.c.
2. Weigh out glucose, 20 grammes (= 2 per cent.) , and dissolve in the hot gelatine. [Pg 185]
3. Filter through papier Chardin. ”

“ The vegetable kingdom furnishes numerous compounds, known as glucosides, which are capable of definite and distinctive fermentations, one of the fermentation products in each instance being sugar. A number of these glucosides are found in fruits. One of the most important of these is amygdalin, a glucoside found in the fruits, leaves, etc., of plants of the almond family, especially in the kernels of the bitter-almond, peach, and cherry, the leaves of the cherry-laurel, and the bark of the wild-cherry. ”

“ The production of a substance known as fat or oil, composed of oxygen, hydrogen, and carbon in the form of a fatty acid and combined with glycerine, is a function of almost every plant. The fat acids are usually in combination with glycerine, which plays the part of a base and in so far as its proportion by weight is concerned is much less important than the fatty acid itself. In round numbers it may be said that nine-tenths of all glycerids or fats are composed of a fatty acid and one-tenth of glycerine. ”

“ Glucose, which is abundant in the juice of plants and fruits, and to a more or less degree in the blood of all animals (usually about 0.1%) occurs free in nature. This sugar is likewise obtained from many carbohydrates, either through the action of acids, or as the result of the digestive enzymes, and as such becomes the principal form in which the animal body utilizes the carbohydrates ingested. Under normal conditions the glucose in the blood is constantly being burned and replaced ”