Full resolution (JPEG) - On this page / på denna sida - II. The Protein 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.
NITROGEN DISTRIBUTION. 79
By the action of nitrous acid upon proteins at least a partial deamidation
takes place and so-called desamino proteins arc obtained. The nitrogen expelled
originated from the XII,. groups according to the formula RNHi+HNOj=»ROH+
Xj+IIjO. The amount of such nitrogen is generally only small, 1-2 per cent,
and for this reason it has been accepted thai such groups only occur in small
amounts in the proteins. This is probably true for a large number of proteins
but not for all and as example of these we will recall that Kossel and CAMERON ’
have shown that those protamines which contain no other hexone base besides
arginine although they have NHa groups at the ends in the guanidine residue
HN.CNH.NHj of the numerous arginine groups, do not yield any nitrogen on
Using v. Sltke’s method while those protamines containing lysine do. We must
be very careful in drawing certain conclusions from the results obtained by the
action of nitrous acid upon proteins.
The nitrous acid can develop nitrogen from the XTH2 groups of the acid amides
as well as from the XH2 groups of the amino-acids. On the contrary no nitrogen
is evolved in v. Slyke’s method from the guanidin groups and from the peptic!
combinations containing imid groups (see below). This is also the reason, as
remarked above, why those protamines containing only arginine do not jdeld
any nitrogen while those protamines which also contain lysine where there exist
free XH2 groups do give off nitrogen. On hydrolyzing these deamidized pro-
tamines and also other deamidized proteins we therefore do not obtain any lysin
as shown by Skraup and collaborators and by Levites for certain proteins.
The quantity of monamino-acid nitrogen is therefore in such cases found to be
increased.
According to Osborne, Leavenworth and Brautlecht, 2
who worked
with plant proteins, the splitting off of XH3 on the acid hydrolysis of the proteins
was very similar to the splitting off of XT
H3 from the acid amide asparagine, so
that the binding of XH2 groups on the carboxyl groups seems very probable.
The quantity of NH3 split off in the hydrolysis ran parallel With the amount
of asparagine and glutamic acid present and the quantity of XH3 , split off by
hydrolysis with alkali corresponded nearly to the sum of the ammonia that was
split off by acid hydrolysis and one-half of the arginine nitrogen. According to
these investigators the XH2 groups occur chiefly as acid-amide combinations.
A part of the nitrogen in the proteins occurs from the above, undoubt-
edly as NH2 groups; the extent of this part, which is different in different
proteins cannot be positively given. The chief mass of the nitrogen
in the proteins, although other forms of binding occur, exists as imide-
like combinations of amino-acids united together and this will be com-
pletely developed in the following pages.
The sulphur occurs in the different proteins in very different amounts.
Certain of them, such as the protamines and apparently also certain
1
In regard to the action of nitrous acid upon proteins, their deamidation and cleav-
age products see C. Paal, Ber. d. d. Chem. Gesellsch., 29; H. Schiff, ibid., 1354; 0.
Loew, Chemiker Ztg., 1896 and O. Nasse, Pfliiger’s Arch., 6; Treves and Salomone,
Bioch. Zeitschr, 7; Skraup, Monatsh. f. Chem., 27 and 28, with Hoernes, ibid., 27,
with Kaas, Annal. d. Chem. u. Pharm., 351; Lampel, Monatsh. f. Chem., 28; Traxl,
ibid., 2ft; Levites, Zeitschr. f. physiol. Chem., 43, and Bioch. Zeitschr., 20; D. v.
Slyke, foot-note 4, page 78; Kossel and Cameron, Zeitschr. f. physiol. Chem., 76; Kossel
and F. Weiss, ibid., 78.
2
Amer. Journ. of Physiol., 23.
<< prev. page << föreg. sida << >> nästa sida >> next page >>
