This study has confirmed the existence of
pepsinogen D in extracts of pig gastric mucosae. It
is present to the extent of about 5% of the potential
proteolytic activity in extracts of the body regions of
pooled gastric mucosae of a number of pigs and from the
gastric mucosa of only one pig.
The conditions required for the chromatographic
isolation of pepsinogen D have been defined more precisely, and as a result it can be isolated with a purity which is probably greater than 95%.
Pepsinogen D is present to the extent of about 15%
in extracts of the pyloric regions of pig stomachs but
the total yield of zymogen is so small as to make this
an unfavourable source of the zymogen.
Studies on pepsinogen D have shown it, like
pepsinogen, to have a molecular weight of about 41,000
and to have one amino -terminal leucine and one carboxyl - terminal alanine residue per mole. It does not contain
phosphorus in phosphodiester linkage and analysis of the
peptides obtained after digestion of the performic acid
oxidised protein with a- chymotrypsin indicate that it is
very similar to or identical with dephosphopepsinogen.
Pepsinogen D also behaves in a similar manner to
dephosphopepsinogen on chromatography on DEAE- cellulose
at pH 6.9 and on electrophoresis in starch gel at pH 3.2.
Like pepsinogen, pepsinogen D is activated at pH 3.7
in accordance with autocatalytic kinetics, although at
pH 4.6 it is activated more slowly than is the main
On exposure to alkali, the potential ability of
pepsinogen D to digest haemoglobin declines in a way
which is similar to that of pepsinogen although its
ability to digest N- acetyl -L- phenylalanyl -L -di- iodotyrosine is much more stable.
Pepsin D, the enzyme produced by activation of
pepsinogen D, has been found to occur in commercial
preparations of both crude and crystalline pepsin to the
extent of about 10j0, and a method has been developed for
its isolation by chromatography on DEAE- cellulose at
Like pepsin, pepsin D has a molecular weight of
about 35,000 and, while it is also similar in having the
carboxyl- terminal sequence.... Val. I -leu. AlaCOOH, it
differs in having an amino -terminal leucine residue and
no, phosphorus which is bound in phosphodiester linkage.
Pepsin D is similar to pepsin in its ability to
digest haemoglobin, N- acetyl -L- phenylalanyl -L -diiodotyrosine and gelatin but its specific activity in the
clotting of milk is twice that of pepsin. Its
specificity in digestion of the B -chain of oxidised
insulin cannot, however, be distinguished from that of
Activation of pepsinogen D produces a peptide which
inhibits pepsin and pepsin D to the same extent as the
peptide inhibitor produced by the activation of
It was concluded that pepsinogen D was very similar
to or identical with dephosphopepsinogen and that it
gives rise on activation to an inhibitory peptide and an
enzyme the latter of which is similar to although not
identical with dephosphopepsin.