Corpuscular proteins

In the following chapters attention will in the main be directed to the charged macromolecules of the statistical skein type not because the corpuscular proteins would be less important, quite the contrary, but because various excellent monographs on proteins have appeared recently and they deal with this group of substances much more extensively than would be possible here. 

We shall occupy ourselves in the following pages mainly with the natural and a few modified natural colloids, whereby, as we have already mentioned, the corpuscular proteins will be practically left out of consideration. 

In the first place we give some comparisons between the electrophoretic velocity of corpuscular proteins in solution and of the same proteins absorbed on various particles under the same conditions as regards pH and salt concentration. It appears that in various cases these two E.V. are identical (serum albumin. Fig. 5, pseudoglobulin, Fig. 6) and that in a case such as ovalbumin (Fig. 7) where a definite difference... 

Next, it is worth while comparing the data from titration curves with those from electrophoresis. Here again the best investigations have been made on corpuscular proteins. A beautiful example is to be found in the work of Cannan, Kibrick and Palmer on the titration and that of Longsworth on the electrophoresis of ovalbumin. 

THE UNIQUE POSITION OF THE CORPUSCULAR PROTEINS CRYSTALLISATION AND DENATURATION... 

Globular or better Corpuscular" proteins, as already discussed earlier (Ch. VII 1 b p. 185), occupy a position apart among the macromolecular colloids, because in them the kinetic unit consists of a tightly built corpuscle, or of an association or binding of numerous such corpuscles (submolecules), with a very specific structure. One can assume that in these corpuscular proteins the macromolecules are folded in a very specific manner into dense structural units. 

In the first place the nature of the colloid-rich phase which separates when the conditions are such that it is obtained in the low dispersed form. Then corpuscular proteins usually give colloid crystals, the other macromolecular colloids however giving coacervates. Secondly the frequent occurrence of irreversible changes of solubility in corpuscular proteins, which as a rule are absent in the other macromolecular colloids (or if present are based on quite different causes ). 

The first of these differences can be sought in the ease with which these tightly built kinetic units of the corpuscular proteins can be fitted into a three-dimensional lattice on account of their well-defined three-dimensional dimensions while it seems very improbable that this would occur spontaneously when the kinetic units consist of randomly kinked macromolecules. 

One can hardly think of these kinetic units of the corpuscular proteins being stable otherwise than when lateral bonds (primary or secondary valencies) between groups of contiguous folds of the macromolecule or between subunits counteract to a sufficient extent the natural tendency of the long chain molecule to assume the most probable shape, that of the randomly kinked macromolecule. 

Only a few cases are known in which corpuscular proteins separate in the form of drops. One can in these cases merely doubt whether these are really true coacervates, that is to say, amorphous colloid-rich liquids. Compare the example discussed later on, edestin on p. 241 (this ). 

These and other results show that protein crystals must really be considered as true crystals to the extent that the corpuscular protein molecules are arranged in them in a three-dimensional lattice and that the mother liquor is essential for their integrity. 

Just as also in the world of the micro-units phases are known which in their degree of order occupy a place in between the crystalline and the liquid, so one also finds them with some corpuscular proteins with very extended molecules. Under various conditions tobacco mosaic virus protein can be precipitated from its solution in the form of fibrous aggregates which were first looked upon as crystals but on closer investigation proved. to be paracrystals. 

With the corpuscular protein, egg albumin, [ly] is low and nevertheless it forms completely stable solutions. The solubility of macromolecular colloids thus cannot depend on the acquirement of thick solvate coatings and with this the starting point of the original coacervation theory is nul and void. 

Before attempting to give a new interpretation of the typical coacervation of macromolecular colloids in the following pages, we wish also to point out that no good examples are yet known to us in which a genuinely liquid coacervation of corpuscular proteins occurs Under circumstances in which this could be expected, for example with (NH4)2 SO4, either crystallisation or a so-called amorphous flocculation occurs. 

Only the "amorphous flocculation of corpuscular proteins could still be represented by Fig. 7 in so far as the separated highly dispersed colloid-rich phase is not microcrystalline or paracrystalline, if at any rate one replaces the very great hydration by a suitably smaller one, similarly the spheres by appropriately shaped corpuscles and thinks of these as placed in the "coacervate at short distances from each other but in such a way that there is still no question of a rigorous order... 

Genuinely liquid coacervates can indeed be produced in which a macromolecular colloid of the linear type takes part besides a corpuscular protein, for example, the complex-coacervation of serum albumin (positive) — gum arabic (negative). See p. 233, Fig. 2. 

Taking into consideration that all these different ionogenic groups each characterised by its specific properties, if situated at the surface of the corpuscular macromolecule, may occupy different relative positions, it will be evident that the corpuscular proteins cannot at all be considered as a simple case, suitable for startii a discussion on the significance of characteristic charge elements. 

As, however, the globulins belong to the class of corpuscular proteins, which have been excluded from treatment in this book, we will not enter further into these problems (for extra complications see p. 261-262). 

A test of eq (6), that has to be carried out with particles in overwhelming Brown-ian motion, can only be given with much smaller particles Simha compares axial ratio s of corpuscular proteins as derived from viscosity measurements (eq (6)) with the axial ratio as determined from the combination of sedimentation and diffusion experiments or from electron microscopic measurements On the whole the accordance is excellent See Table 1 ... 

Axial rations of corpuscular proteins determined by viscosity measurements according to bq. 

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