Mar. 15, 1925 
Polypeptides and Amino Acids in Maize Kernel 
589 
Experiments conducted with the 
three corn varieties in order to ascer¬ 
tain how best to extract the nitrogen 
of the corn flour have shown that the 
nitrogen extracted by water at room 
temperature in one hour is as great as 
that obtained in two and four hours, 
respectively. In this connection it was 
found, as would be expected, that a 
cold aqueous extract of the flour is 
absolutely free from starch and is very 
convenient to handle, while a hot 
aqueous extract contains great quan¬ 
tities of starch and is considerably 
harder to handle. Since the data con¬ 
cerning the extraction of the flour with 
w'ater are quite uniform, they are 
omitted here to save space. It may 
suffice to mention that in the experi¬ 
ments reported subsequently definite 
amounts of flour with measured quan¬ 
tities of water were agitated by means 
of a shaking machine for one hour at 
room temperature, an antiseptic being 
used to prevent bacterial action. 
The extract obtained was freed from 
starch, proteins and other insoluble 
substances by filtration, the filtrate 
concentrated in vacuo , any precipitates 
formed during concentration were re¬ 
moved by centrifugation, the super¬ 
natant liquid evaporated to dryness, 
and the residue extracted with 80 per 
cent alcohol, filtered and the alcohol 
distilled off. The residual yellow sirup 
was dissolved in hot water, heated to 
boiling, acidified with acetic acid, 
boiled, and filtered, the filtrate treated 
with freshly made lead hydroxide and 
some lead acetate, and again boiled and 
filtered. This filtrate was now concen¬ 
trated under reduced pressure to a 
small volume. 
It should be borne in mind, however, 
that a water-extract of seeds, prepared 
in the cold, usually contains proteo¬ 
lytic enzymes which may in part hydro¬ 
lyze the proteins and proteoses present 
in the maize kernel. For this reason 
it seemed necessary to carry out paral¬ 
lel experiments under conditions which 
destroy the enzymes completely, in 
order definitely to decide whether or 
not the amino acids and polypeptides 
are preformed in the maize kernel. 
Hence weighed quantities of flour were 
treated in flasks with boiling hot am¬ 
monia-free water and kept on the water 
bath for about half an hour, whereupon 
their contents were contrifuged. The 
solid residue was then treated in the 
same way once more. The hot water- 
extracts thus obtained were then 
treated essentially as described above. 
The concentrated purified extracts ob¬ 
tained were applied to the estimation 
of the acid amides, amino acids, and 
polypeptides. 
In order to determine the nitrogen 
of acid amides, the purified extract cor¬ 
responding to a definite quantity of 
flour was made up to 100 c. c., of which 
two portions of 20 c. c., each were 
oxidized according to Kjeldahl’s method 
to ascertain the amount of nitrogen 
present. To 50 c. c. of the remaining 
solution hydrochloric acid was added to 
a concentration of 20 per cent and 
boiled for 30 minutes using a reflux 
condenser. The hydrolysate was evap¬ 
orated on the water bath to dryness, 
the residue transferred quantitatively 
to a Kjeldahl flask and distilled with 
magnesium oxide, the ammonia thus 
obtained being titrated with standard 
acid. 
For the estimation of the nitrogen of 
amino acids and of polypeptides a 
sufficient quantity of the purified ex¬ 
tract, at least twice the amount used 
for the acid amide determination, was 
made up to 200 c. c., in two 10 c. c. 
portions of which the nitrogen was esti¬ 
mated according to the Kjeldahl 
method. The remaining 180 c. c. were 
made up to 200 c. c. and divided into 
100 c. c. portions a and b. In portion a , 
freed from carbon dioxide, phosphoric 
acid, and coloring matter, the amino 
nitrogen was determined by the formol- 
titration method (16), while portion b 
was employed for the estimation of the 
peptide nitrogen. Enough hydrochloric 
acid was added to portion b to make a 
20 per cent solution and boiled under a 
reflux condenser for 12 hours, in accord¬ 
ance with the observations of Fischer 
(4, V . 53 ). The hydrolyzed material was 
then evaporated on the water bath to 
dryness, transferred to a Kjeldahl flask, 
to which magnesium oxide was added 
and the ammonia expelled by distilla¬ 
tion. The residue was then thoroughly 
extracted with boiling hot ammonia-free 
water and the filtered extract concen¬ 
trated to 100 c. c. of which two portions 
of 20 c. c. each were oxidized according 
to the Kjeldahl method, while 50 c. c. 
of the remaining liquid were used for 
formol-titration. The result obtained 
here by titration with formaldehyde 
diminished by the amino nitrogen 
secured prior to the hydrolysis yields 
the nitrogen of the polypeptides. The 
data are recorded in Table II. 
Examination of Table II shows that 
the highest proportion of the nitrogen 
of acid amides and polypeptides is 
found in Four County corn, while the 
highest proportion of amino nitrogen 
is contained in Hall Gold Nugget 
selection 193, when the latter is re¬ 
ferred to the oven-dried kernel and 
to its total nitrogen. The figures for 
United States selection 77 fluctuate, 
some higher and some lower than for 
19975—25t-7 
