ON THE NATURE OF THE SUGAR IN BLOOD.
BY L. B. WINTER, B.A. AND W. SMITH, B.A.
(From the Biochemical Laboratory, Cambridge.)
THE experiments of Minkowsky(') first established the importance
played by the pancreas in the metabolism of carbohydrate. Clark(<)
showed that the consumption of sugar by the heart was increased when
the perfusing fluid was also passed through the pancreas. In a later
paper(3) he established the remarkable fact that perfusion of the pancreas
with Locke's solution, i.e. one containing dextrose caused the optical
rotation to be diminished whereas the copper reducing value remained
unaltered. He suggested that the pancreas contained an enzyme which
was responsible for converting dextrose into another form of sugar, which
then could be utilised by the body.
The recent work of Embden and his co-workers(4) has emphasised
the importance of hexose-phosphoric acid in the carbohydrate meta-
bolism of muscle. Since on hydrolysis hexose-phosphoric acid yields
fructose, it seemed possible that the sugar in normal blood might be
other than glucose. The primary aim of our experiments-begun in 1921
-was, then, to investigate the nature of the sugar in the blood by a
comparison of the polarisation, and copper reducing values. For this it
was necessary to prepare a protein-free filtrate.
After testing the various protein precipitation methods usually
employed for blood sugar estimations, we found that they all gave on
concentration a fluid which was quite unsuitable for polarimetric deter-
mination. The tungstic acid method of Folin and WU(5) was least
tedious, and gave a filtrate which was almost free from the precipitant;
that all protein was not removed was made clear by nitrogen determina-
tions, and by the turbidity which appeared when the filtrate was con-
centrated to a small bulk. It was necessary, therefore, to employ some
further process in order to remove the remainder of the proteins and to
extract the sugar. The use of alcohol in a suitable strength to effect both
processes simultaneously suggested itself. In a series of trials 85 p.c.