Chemical pathology : being a discussion of general pathology from the standpoint of the chemical processes involved / by H. Gideon Wells.

  • Wells, H. Gideon (Harry Gideon), 1875-1943.
Date:
1918
Catalogue details

Licence: In copyright

Credit: Chemical pathology : being a discussion of general pathology from the standpoint of the chemical processes involved / by H. Gideon Wells. Source: Wellcome Collection.

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    the formation of glycylglycine, an acid radical and a basic radical are still left free. In this may be seen the explanation of the peculiar amphoteric nature of proteins. As long as these two groups are free the proteins can combine with either acids or bases, as they are well known to do, and hence they react as either acids or bases under dif- ferent conditions. It must not be imagined that the structure of the complete mole- cule is simply a long straight chain of amino-acids joined only in the same way as are the components of glycylglycine. The existence of the diamino-acids, of the benzene rings, of hydroxyl groups, (as in serine or tyrosine), of ring compounds, (as pyrrolidine carboxylic acid), of substances with two acid groups, (as glutaminic and aspar- tic acid), adds complications to the formation until it is impossible to estimate just how all the various building stones may be arranged. We must bear in mind the size of the protein molecule, which Hof- meister has estimated (for serum albumin) as having a molecular weight of 10,166, and for hemoglobin the molecular weight has been estimated at 16,669.4 Within such a “giant molecule” there is room for variety almost beyond computation. The Proteins of the Cell.—By physiological chemists proteins are classified into simple proteins, of which egg and serum albumin are types; and compound proteins, which are characterized by having some special non-protein group which can be split off, leaving behind a characteristic protein residue, e. g., nucleo-proteins, glyco-proteins. As primary cell constituents the following varieties of proteins may be mentioned; albumin, globulin, nucleo-protein, nucleo-albumin or phospho-protein, and insoluble proteins. At one time it was thought that cytoplasm consisted chiefly of albumin, like white of egg, but we now know that this forms but a small part of the cell proteins, often occurring only as traces. It is held by some that true albumin occurs only as a building or intermediate cleavage product of the more complicated forms of cellular proteins, and is itself of relatively slight importance in cell life, not participating in chemical changes except as a food-stuff. Albumins are characterized chiefly by their greater solubility in water, and in being less easily precipitated than most proteins. They seem to be a fundamental type of proteins. The three forms of al- bumin that have been described in animal tissues or products are egg- albumin, lactalbumin of milk, and serum albumin; probably cell al- bumin is most closely related to the last, and what has been described as cell albumin is perhaps in many cases but serum albumin that has been imperfectly removed. 4 Robertson (Jour. Biol. Chem., 1909 (6), 105) suggests that these high molec- ular weights represent polymerization, the single protein molecules being much smaller; casein salts in neutral solutions have a molecular weight of but 2000, according to his investigations.