426 Yeast Nucleic Acid. III 
salt was separated into two fractions, one analyzing for uridinephos- 
phoric acid, the other for adenosinephosphoric acid. Out of 120 
gm. of the mixed salt there were obtained 50 gm. of the first 
portion and 70.0 gm. of the second. ‘The first salt was converted 
into a barium salt which possessed the crystal form, the optical 
rotation, and the analytical values of the recently described® 
barium salt of uridinephosphorie acid. 
The second fraction was also converted into a barium salt 
which separated out of a concentrated aqueous solution. How- 
ever, it was impossible thus far to obtain the salt in crystalline 
form. Work in this direction is in progress. 
It is evident on the basis of this experience that as far as the 
yeast nucleic acid is concerned the largest fragment obtained up 
to the present is a mononucleotide. Hence the problem of the 
mode of linkage between the individual nucleotides still awaits 
its solution. On the other hand the work done in Jones’ labora- 
tory and our recent work have advanced further proof for the 
tetranucleotide structure of yeast nucleic acid, since on cleavage 
of the nucleic acid it is now possible to isolate the following three 
mononucleotides in pure form: guanylic acid, uridinephosphoric 
acid, and cytidinephosphoric acid; and there is reasonable hope 
that adenosinephosphoric acid also will be prepared in pure form. 
EXPERIMENTAL. 
Crude nucleic acid in lots of 100.0 gm. each in 500 cc. of water 
aitd 50 cc. of 25 per cent ammonia water were hydrolyzed for 1 
hour in an autoclave at 115°C. The reaction product was fil- 
tered and to the filtrate an equal volume of 98 per cent alcohol 
was added. A precipitate was thus formed which was removed by 
filtration. The filtrate was concentrated to a third of the origi- 
nal volume under diminished pressure (between 12 and 15 mm.), 
the temperature of the water bath not exceeding 40°C. To the 
concentrated solution was added again an equal volume of 98 
per cent alcohol. To the filtrate a 25 per cent solution of basic 
lead acetate was added as long as a precipitate formed. 
The lead precipitate was ground up in a solution containing 5 
per cent lead acetate and filtered. The operation was repeated 
three times. The washed lead precipitate was suspended in water 
5 Levene, P. A., J. Biol. Chem., 1918, xxxili, 229. 
