On Digestive Proteolysis / Being the Cartwright Lectures for 1894

by R. H. Chittenden

Composition of Some of the More Prominent Proteids Occurring in Nature.*

Substance.	C	H	N	S	O	P	Ash.		Origin.	Author.
Serum-albumin	63.05	6.85	16.04	1.77	22.29	....		0.57—	Serum from horse blood	Hammarsten.[54]
Serum-albumin	52.25	6.65	15.88	2.27	22.95	....		1.84	Pleural exudation	Hammarsten.[54]
Egg-albumin	52.25	6.90	15.25	1.93	23.67	....		....	Non-coagulated	Hammarsten.[54]
Egg-albumin	52.33	6.98	15.89	1.83	22.97	....		1.11	Non-coagulated	Chittenden and Bolton.[55]
Lacto-albumin	52.19	7.18	15.77	1.73	23.13	....		....	Cow’s milk	Sebelien.[56]
Vegetable-albumin	52.25	6.76	16.07	1.48	23.44	....		0.70	Corn or maize	Chittenden and Osborne.[57]
Vegetable-albumin	53.02	6.84	16.80	1.28	22.06	....		0.82	Wheat	Osborne and Voorhees.[58]
Proteose, animal	52.13	6.83	16.55	1.09	23.40	....		0.79	Hemialbumose, urine	Kühne and Chittenden.[59]
Proteose, vegetable	60.60	6.68	16.33	1.62	24.77	....		2.99	Corn or maize	Chittenden and Osborne.[57]
Proteose, vegetable	51.86	6.82	17.32	....	....	....		0.25	Wheat	Osborne and Voorhees.[58]
Proteose, vegetable	49.98	6.95	18.78	....	....	....		1.80	Flax-seed	Osborne.[60]
Proteose, vegetable	46.52	6.40	18.25	....	....	....		2.20	Cocoanut meat	Chittenden and Setchell.[61]
Vitellin, spheroidal	51.71	6.84	18.12	0.85	22.48	....		1.20	Corn or maize	Chittenden and Osborne.[57]
Vitellin, crystalline	51.60	6.97	18.80	1.01	21.62	....		0.30	Squash-seed	Chittenden and Hartwell.[62]
Vitellin, amorphous	51.81	6.94	18.71	1.01	21.53	....		0	Squash-seed	Chittenden and Hartwell.[61]
Vitellin, crystalline	51.48	6.94	18.60	0.81	22.17	....		0.54	Flax-seed	Osborne.[60]
Vitellin, spheroids	51.03	6.85	18.39	0.69	23.04	....		0.49	Wheat	Osborne and Voorhees.[58]
Vitellin, crystalline	51.63	6.90	18.78	0.90	21.79	....		0.56	Hemp-seed	Chittenden and Mendel.[61]
Vitellin, crystalline	51.31	6.97	18.75	0.76	22.21	....		0.03	Castor bean	Osborne.[63]
Vitellin, crystalline	52.18	6.92	18.30	1.06	21.54	....		0.20	Brazil nut	Osborne.[63]
Vitellin, semi-crystalline	51.23	6.90	18.40	1.06	22.41	....		0.25	Cocoanut meat	Chittenden and Setchell.[61]
Myosin, 13 different samples	52.82	7.11	16.77	1.27	21.90	....		1.45	Muscle-tissue	Chittenden and Cummins.[64]
Myosin, vegetable	52.68	7.02	16.78	1.30	22.22	....		0.63	Corn or maize	Chittenden and Osborne.[57]
Myosin, vegetable, crystalline	52.18	7.05	17.90	0.53	22.34	....		0.10	Oats	Osborne.[65]
Paraglobulin	52.71	7.01	15.85	1.11	23.24	....		0.30	Blood of horse	Hammarsten.[66]
Fibrinogen	52.93	6.90	16.66	1.25	22.26	....		1.75	Blood of horse	Hammarsten.[67]
Zein	55.23	7.26	16.13	0.60	20.78	....		0.43	Corn or maize	Chittenden and Osborne.[57]
Gliadin	52.72	6.86	17.66	1.14	21.62	....		0.51	Wheat	Osborne and Voorhees.[58]
Gliadin	53.01	6.91	16.43	2.26	21.39	....		....	Oats	Osborne.[65]
Glutenin	52.34	6.83	17.49	1.08	22.25	....		....	Wheat	Osborne and Voorhees.[58]
Coagulated proteid	52.33	6.98	15.84	1.81	23.04	....		0.27	Egg-albumin	Chittenden and Bolton.[55]
Coagulated proteid	51.58	6.88	18.80	1.09	21.65	....		0.25	Vitellin, hemp-seed	Chittenden and Mendel.[61]
Fibrin	52.68	6.83	16.91	1.10	22.48	....		0.56	Blood of horse	Hammarsten.[67]
Oxyhæmoglobin	53.85	7.32	16.17	0.39	21.84	....		0.43 Fe.	Blood of dog	Hoppe-Seyler.[68]
Oxyhæmoglobin	54.71	7.38	17.43	0.48	19.60	....		0.39 Fe.	Blood of pig	Hütner.[69]
Mucin	50.30	6.84	13.62	1.71	27.53	....		0.33	From snail	Hammarsten.[70]
Mucin	48.84	6.80	12.32	0.84	31.20	....		0.35	Submaxilliary gland	Hammarsten.[71]
Chondromucoid	47.30	6.42	12.58	2.42	31.28	....		....	Cartilage	Mörner.[72]
Nuclein	50.60	7.60	13.18	....	....	1.89		....	Human brain	V. Jaksch.[73]
Nuclein	49.58	7.10	15.02	....	....	2.28		....	Pus	Hoppe-Seyler.[74]
Casein	52.96	7.05	15.65	0.71	22.78	0.84		....	Cow’s milk	Hammarsten.[75]
Casein	53.30	7.07	15.91	0.82	22.03	0.87		0.98	Cow’s milk	Chittenden and Painter.[76]
Nucleo-histon or leuconuclein	48.41	7.21	16.85	0.70	24.41	2.42		....	Leucocytes	Lilienfeld.[77]
Gelatin	49.38	6.81	17.97	0.71	25.13	....		1.26	Connective tissue	Chittenden and Solley.[78]
Elastin	54.24	7.27	16.70	0.30	21.79	....		0.90	Neck-band	Chittenden and Hart.[79]
Elastin	53.95	7.03	16.67	0.38	21.97	....		0.72	Aorta	Schwarz.[80]
Keratin	49.45	6.52	16.81	4.02	23.20	....		1.01	White rabbit’s hair	Kühne and Chittenden.[81]
Neurokeratin	56.99	7.53	13.15	1.87	20.46	....		1.35	Human brain	Kühne and Chittenden.[82]
Reticulin	52.88	6.97	15.63	1.88	22.30	0.34		2.27	Reticular tissue	Siegfried.[83]

* Many of these results represent the average of a large number of individual analyses.

In considering the results tabulated above, it is to be remembered that all of these bodies, with the exception of keratin, neurokeratin, and reticulin, are more or less digestible in either gastric or pancreatic juice, or indeed in both fluids. I will not take time here to point out the obvious genetic relationships and differences in composition shown by the above data, but will immediately call your attention to the fact that there are other and more important points of difference between many of these proteids which are hidden beneath the surface, and which a simple determination of composition will not bring to light. I refer to the chemical constitution of the bodies, to the way in which the individual atoms are arranged in the molecule, on which hinges more or less the general properties of the bodies and which in part determines their behavior toward the digestive enzymes, as well as toward other hydrolytic agents. These differences in inner structure can only be ascertained by a study of the decomposition products of the proteids, and of the way in which the complex molecules break down into simpler. The nature of the fragments resulting from the decomposition of a complex proteid molecule, gives at once something of an insight into the character of the molecule. Thus, egg-albumin exposed to the action of boiling dilute sulphuric acid yields, among other fragments, large quantities of leucin and tyrosin, the latter belonging to the aromatic group and containing the phenyl radical. Collagen, or gelatin, on the other hand, by similar treatment fails to yield any tyrosin or related aromatic body, but gives instead glycocoll or amido-acetic acid, in addition to leucin, lysin, and other products common to albumin. Its constitution, therefore, is evidently quite different from that of albumin, but the composition of the body reveals no sign of it. Further, we have physiological evidence of this difference in constitution in that gelatin, though containing even more nitrogen than albumin, is not able to take the place of the latter in supplying the physiological needs of the body; its food-value is of quite a different order from that of albumin.

But while all of the individual proteids show many points of difference, either in composition, constitution, reactions, or otherwise, they are nearly all alike in their tendency to undergo hydrolytic decomposition under proper conditions; the extent of the hydrolysis and accompanying cleavage being dependent simply upon the vigor or duration of the hydrolytic process.

Furthermore, all of the simple proteids, at least, give evidence of the presence of two distinct groups or radicals, which give rise by decomposition or cleavage to two distinct classes of products. These two groups, which we may assume to be characteristic of every typical proteid, Kühne has named the anti- and hemi-group respectively. This conception of the proteid molecule is one of the foundation-stones on which rest some of our present theories regarding the hydrolytic decomposition of proteids, especially by the proteolytic enzymes. Moreover, it is not a mere conception, for it has been tested so many times by experiment that it has seemingly become a fact. The two groups, or their represen­ta­tives, can be separated, in part, at least, by the action of dilute sulphuric acid (three per cent.) at 100° C. Thus, after a few hours’ treatment of coagulated egg-albumin, about fifty per cent. of the proteid passes into solution, while there remains a homogeneous mass, something like silica in appearance, insoluble in dilute acid, but readily soluble in dilute solutions of sodium carbonate. This latter is the representative of the anti-group, originally named by Schützenberger[84] hemiprotein, but now called antialbumid.[85] It is only slightly digestible in gastric juice, but is readily attacked by alkaline solutions of trypsin, being converted thereby into a soluble peptone known as antipeptone. In the sulphuric acid solution, on the other hand, are found the represen­ta­tives of the hemi-group; viz., albumoses, originally known as one body, hemialbumose,[86] together with more or less hemipeptone, leucin, tyrosin, etc.

The fact that we have so many represen­ta­tives of the hemi-group in this decomposition is significant of the readiness with which the so-called hemi-group undergoes change. All of its members are prone to suffer hydration and cleavage, passing through successive stages until leucin, tyrosin, and other simple bodies are reached. These, and other similar crystalline bodies, are likewise the typical end-products of proteolysis by trypsin, and presumably come directly from the breaking-down of hemipeptone. Antipeptone, on the other hand, is incapable of further change by the proteolytic ferment trypsin. Hence, the hemi-group can be identified by the behavior of the body containing it toward trypsin; i.e., it will ultimately yield leucin, tyrosin, and other bodies of simple constitution to be spoken of later on. The anti-group, however, will show its presence by a certain degree of resistance to the action of trypsin, antipeptone being the final product of its transformation by this agent; i.e., leucin, tyrosin, etc., will not result. In this hydrolytic cleavage of proteids the anti-group does not always appear as antialbumid. It may make its appearance in the form of some related body, the exact character of the product being dependent in great part upon the nature of the hydrolytic agent, but in every case the character­istics of the anti-group will come to the surface when the body is subjected to the action of trypsin.

The above-described treatment of a coagulated proteid with water containing sulphuric acid evidently induces profound changes in the proteid molecule. The conditions are certainly such as favor hydration, and in the case of complex molecules, like the proteids, cleavage might naturally be expected to follow. Analysis of antialbumid from various sources plainly shows that its formation is accompanied by marked chemical changes. Thus, the following data, showing the composition of antialbumid formed from egg-albumin and serum-albumin by the action of dilute sulphuric acid at 100° C., gives tangible expression to the extent of this change:

	Egg-albumin.	Antialbumid[87] from egg-albumin.	Serum-albumin.	Antialbumid[87] from serum-albumin.
C .......	52.33	53.79	53.05	54.51
H.......	6.98	7.08	6.85	7.27
N .......	15.84	14.55	16.04	14.31