To: Professor Pauling From: Walter Schroeder Date: November 6, 1952
I would like to present a resumé of amino acid analyses of gelatin and collagen as
they are to be found in recent literature. The data are recorded in the attached table.
Sources and Presentation of Data
The date listed under “Neuman” are taken from papers by Neuman (Arch. Biochem., 24,
289 (1949)) and Neuman and Logan (J. Biol. Chem., 184, 299 (1950)). In these papers,
complete analyses are listed for 4 gelatins, 12 collagens, and 6 elastins from various
mammalian, avian, end marine sources. In summarizing these values for the attached
table, the elastins as well as the marine gelatin and collagen have been omitted;
the marine materials differ appreciably in certain amino acids. The table lists the
averages from 3 gelatins and 11 collagens and also the extreme values which Neuman
gives for proline, hydroxyproline , and glycine. Neuman has made these analyses in
the main by microbiological procedures but has also used chemical and colorimetric
methods. Hydroxylysine is assumed to be 1 g. per 100 g. protein.
The data listed under “Tristram” are his compilation (Adv. Prot. Chem., 5, 143 (1949))
of the results of Chibnall and of Bowes and Kenten.
The table also includes a calculation of the residue percentage accounted for by proline,
hydroxyproline, and glycine in the two proteins and a few other values which are to
be found in the literature for these three amino acids.
Comments
It seems reasonable to assume that the data may be in error to ± 5 to 10 percent of
the quantity determined. In very few instances is this conservative estimate of error
exceeded by the differences which are to observed whether one compares Neuman’s and
Tristram’s values for the two proteins individually or whether one compares the two
proteins with each other. The concordance of the results is very gratifying in view
of the fact that the results from more than 15 samples are being compared. It should
also be mentioned that in these analyses essentially all of the nitrogen and weight
of the proteins is accounted for. A few scattered values from the literature agree
well; in the case of hydroxyproline and glycine but those for proline are considerably
higher. The latter were obtained by the Bergmann school by precipitation methods and
are suspect for this reason.
It is reasonable to conclude that the published analyses of gelatin and collagen give
a very good picture of the amino acid composition of these proteins and, furthermore,
that these proteins do not differ appreciably in their amino acid make-up. The average
of all data given by Neumann and Tristram for proline, hydroxyproline , and glycine
in both proteins is as follows:
[Data Table]
In view of this rather extensive body of data, it is doubtful that it would be desirable
or worthwhile for us to embark on a program of determining the amino acid composition
of gelatin and collagen by ion exchange methods. In order to obtain definitive results,
the efforts of two workers for at least six months would be required. If our results
should differ from the data which have been presented, it would probably require much
more work in order to determine the source of the differences.
Walter A. Schroeder
[1 page of data]
