Full resolution (JPEG) - On this page / på denna sida - II. The Protein Substances - II. Compound Proteins - A. Glycoproteins (glucoproteins) - 1. Mucin Substances
<< prev. page << föreg. sida << >> nästa sida >> next page >>
Below is the raw OCR text
from the above scanned image.
Do you see an error? Proofread the page now!
Här nedan syns maskintolkade texten från faksimilbilden ovan.
Ser du något fel? Korrekturläs sidan nu!
This page has never been proofread. / Denna sida har aldrig korrekturlästs.
168 THE PROTEIN SUBSTANCES.
last-mentioned group (haemoglobin and haemocyanine) will be discussed
in a subsequent chapter (Chapter V on the blood).
A. Glycoproteins (glucoproteins) .
Glycoproteins *
are those compound proteins which on decomposi-
tion yield a protein on the one side, and a carbohydrate or derivatives
of this on the other, but no purine bodies. Some glycoproteids are free
from phosphorus (mucin substances, chondroproteins, and hyalogens),
and some contain phosphorus (phosphoglycoproteins).
The glycoproteins free from phosphorus may, as regards the nature
of the carbohydrate groups split off, be divided into two chief groups,
the mucin substances and the chondroproteins. The first yield on hydrolytic
cleavage an amino-sugar, which has been shown to be glucosamine in
all but a few exceptions.2
In the chondroproteins, on the contrary, the
protein is united to chondroitin-sulphuric acid.
1. Mucin Substances.
Compared with the simple proteins the mucin substances are poorer
in nitrogen and as a rule also have considerably less carbon. The carbo-
hydrate complex, whose nature has been shown by the investigations
cf Fr. Muller 3
and his pupils, occurs, so it seems, in the mucin sub-
stances as a polysaccharide related to chitosan, which on hydrolytic
cleavage yields glucosamine (chitosamine), and, at least in most cases,
acetic acid also. The mucin substances differ very markedly among
themselves, hence we divide them into two groups, the mucins and the
mucoids.
The true mucins are characterized by the fact that their natural
1
Abderhalden (Lehrb d. physiol. Chem., 1909, p. 191) has proposed dropping the
name glycoproteids entirely and to consider these bodies as simple proteins, because
it has not been shown that the carbohydrate groups occupy the same relationship
to the protein component that the haemin or the nucleic acid bears to the haemo-
globin or the nuclooprotein molecule. It is possible that this proposition, which is
not applicable to the entire group (including the proteins containing chondroitin-
sulphuric acid) but applies only to the mucin group, will be found in the future to be
correct. It is the opinion of Hammarsten that it is better to wait for further research
in this direction before we drop the generally accepted nomenclature and the usual
subdivisions of the proteins.
2
See Schulz and Ditthorn, Zeitschr. f. physiol. Chem., 29; A. v. Ekenstein and
Blunksma, Chem. Centralbl., 1907. 2. When both carbohydrate groups are simul-
taneously combined in one body, then probably we are not dealing with a chemical
individual, but rather with a mixture.
3
See Fr. Muller, Zeitschr. f. Biologie, 42, which contains all the pertinent litera-
ture, and also L. Langstein, Die Bildung von Kohlenhydraten aus Eiweiss, Ergebnisse
der Physiologie, Jahr. I, Abt. 1.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
