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CASUAL URINARY CONSTITUENTS. 775
R.COOH. The appearance of lactic acid in the urine of rabbits after
feeding alanine is an example of such deamidation. 1
The possibility
is not excluded that in the first place the keto-acid, pyruvic acid,
CH3.CO.COOH, is formed from the alanine and then the lactic acid,
CH3.CHOH.COOH, formed from this as a secondary reduction product.
In agreement with the views of Xeubauer 2
it is now rather
generally conceded that the hydrolytic deamidation is not as important
as the oxidative deamidation, with the formation of keto-acids
R.CH(NH2).COOH+0 = R.CO.COOH+NH3 ,
although this is not the
only possibility. The proofs for the correctness of this view have been
obtained essentially by experiments with aromatic amino-acids and
will be given as examples of such deamidation.
Dakin and Dundley 3 have shown that all a-amino-acids investi-
gated by them can be decomposed under special conditions so that they
to a certain degree yield ammonia and an a-keto-aldehyde.
R.CH.NH2 .COOH->R.CO.CHO+NH3 .
Thus, with alanine, and as the reaction to all appearances is reversible,
they consider the relationship between alanine and lactic acid is as follows -
CH3 .CH.NH2.COOE^CH3.CO.CHO^CH3CHOH.COOH.
They also found it probable, that the a-keto-aldehydes represent the
first step in the demolition of the a-amino-acids whereby the regular
demolition of these acids takes place over the a-keto-acids and not over
oxyacids, which explains also the formation of sugar from certain amino-
acids (over methylglyoxal as intermediary step).
The deamidation after previous oxidation with the formation of
keto-acids has awakened special interest because recently in perfusion
experiments on dog-livers the reverse process, namely a synthesis of amino-
acids from keto-acids (in part also from oxyacids) and ammonia has been
performed (Knoop, Embden and Schmitz, Kondo 4
). Among such
syntheses we can here call attention to the synthesis in the dog-liver
of alanine, phenylalanine and tyrosine from pyruvic acid (also lactic acid),
phenylpyruvic acid and p-oxyphenyl pyruvic acid, or of a-amino-n-butyric
acid from a-keto-butyrie acid (all as ammonium salts).
1
See Langstein and Neuberg, Arch. f. (Anat. u.) Physiol., 1903. Suppl. Bd.
1 Deutsch. Arch. f. klin. Med., 95, and Habilit. Schrift., Leipzig, 1908. See also
further on in regard to the literature on the demolition of the aromatic amino-acids.
3
Journ. of biol. Chem., 14.
4
Knoop, Zeitschr. f. physiol. Chem., 67 and 71; Embden and Schmitz, Bioch.
Zeitschr., 29 and 38; Kondo, ibid., 38.
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