Experiment Station Record, Volume 92, January-June, 1945 Page: 9
The following text was automatically extracted from the image on this page using optical character recognition software:
1945] AGRICULTURAL AND BIOLOGICAL CHEMISTRY 9
thiamine values obtained by this method were between 10 and 15 percent lower
than those obtained by the thiochrome method.
Comparison of thiamine' values by chemical and bioassay methods, E. B.
BROWN, J. C. HAMM, and H. E. HARRISON (Jour. Biol. Chem., 151 (1943), No. 1,
pp. 153-161).--Since preliminary work had shown the original method of Hennessy
and Cerecedo (E. S. R., 82, p. 588) to give values about 20 percent below the bioassay
results, certain modifications of the chemical procedure were developed
which resulted in better agreement, with the chemical values only about 10 percent
lower than those obtained by the bioassay (rat growth) method. The modifications
of the Hennessy and Cerecedo method included definite optimum time intervals
for different steps in the process and a higher temperature (52-55 C.) for the
enzymatic hydrolysis with taka-diastase. Under the conditions employed for the
enzymatic hydrolysis, clarase and polydase preparations were less suitable than the
taka-diastase. Careful preparation of the Decalso by a procedure outlined was
necessary for satisfactory activation for maximum adsorption and elution. It was
particularly necessary to keep the activated Decalso moist in any interval preceding
utilization. The differences in readings due to differences in color between sample
extracts and the standard were corrected by calculating the readings to a standard
transmission reference point. This calculation of readings gave values closer to
bioassay results where sample extracts contained more color than the standard,
thereby affecting the reading of the thiochrome to a greater extent in the sample
than in the standard. It was also found that higher results were obtained for
thiamine by thoroughly washing the residues remaining after hydrolysis of the
sample in order to remove occluded thiamine. This step, however, required extra
time and work.
The irreversible transformation, of dehydroascorbic acid, B. ROSENFELD (Jour.
Biol. Chem., 150 (1943), No. 2, pp. 281-303, illus. 4).-Evidence is presented to indicate
that at a pH of 7 and in the presence of phosphate buffer, the irreversible and
nonoxidative transformation of dehydroascorbic acid probably involves scission of
the 6-carbon chain with the quantitative formation of oxalic acid. In the presence
of oxygen the oxalic acid is.preceded by the formation of an oxalyl compound which
is most likely to be oxalylthreonic acid. For the irreversible transformation to
occur at pH 7, phosphate must be present. Phosphate causes catalytically the
spontaneous formation of oxalic acid, but in the absence of phosphate the 6-carbon
chain remains intact. The catalytic action of phosphate can be effectively replaced
by cyanide. Parallel with the irreversible transformation, the dehydroascorbic
acid undergoes another change involving transformation into two other products,
(1) a reducing compound and (2) an oxidized derivative of dehydroascorbic acid.
This change, though hastened by phosphate and cyanide, does not depend upon their
presence; it probably does not occur in animal tissues since it assumes measurable
proportions only at concentrations > 1 X 10-~ M. The reducing compound persists
in its reducing power in acid solution and shows qualitatively the absorption characters
of ascorbic acid in the ultraviolet region. The oxidized derivative is characterized
by an intense yellow color at pH 7.
It is suggested that in the animal body the metabolic break-down of ascorbic acid
starts with the irreversible transformation to the dehydro vitamin, the concentration
of which will reach but a fraction of the actual ascorbic acid concentration in the
living tissue due to the natural protective system for this vitamin, particularly the
presence of excessive glutathione. The quantitative formation of oxalic acid as part
of the biological degradation of ascorbic acid suggests a possible relationship between
vitamin C metabolism and the normal urinary excretion of oxalic acid. This
assumption is in agreement with the observed facts (1) that oxalate excretion is
independent of the oxalate intake in the food, and (2) that the oxalate excretion in
Here’s what’s next.
This book can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Book.
U.S. Department of Agriculture. Agricultural Research Administration. Office of Experiment Stations. Experiment Station Record, Volume 92, January-June, 1945, book, 1947; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc5064/m1/22/: accessed November 21, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.