From the homogenate of rat submaxillary gland, two kinds of
serine proteinases, named tentatively
proteinases A and B, were isolated and their chemical properties and activities toward rat
kininogens were examined, in comparison with those of
submaxillary kallikrein.
Proteinase A with Mr of 28,200 rapidly cleaved high-molecular-weight (HMW)
kininogen into a
protein of 67 kDa, which retained
thiol-
proteinase inhibitory activity, but had lost the correcting activity of HMW
kininogen on the prolonged clotting time of
Fitzgerald trait plasma. It liberated
bradykinin from HMW
kininogen but did not liberate
kinin from
T-kininogen and did not degrade
T-kininogen. On the other hand,
proteinase B with Mr of 30,400 showed a very weak activity for the liberation of
kinin from
T-kininogen and the cleavage of
T-kininogen at pH 8.0. However, the
enzyme extensively degraded
T-kininogen at pH 4.5.
Proteinase B also degraded HMW
kininogen at pH 4.5 and pH 8.0, but liberated
bradykinin only at pH 8.0.
Thiol-
proteinase inhibitory activities of HMW
kininogen and
T-kininogen were inactivated after the incubation with
proteinase B at pH 4.5 but not at pH 8.0, while the correcting activity of HMW
kininogen on the
Fitzgerald trait plasma was inactivated at pH 4.5 and 8.0. The NH2-terminal amino acid sequences of
proteinases A and B were different from each other, and distinguishable with those of
serine proteinases in rat submaxillary gland so far reported. These results provide evidence that in addition to the known
kallikrein, there exist at least two kinds of
serine proteinases in rat submaxillary gland, both of which liberate
bradykinin from rat HMW
kininogen at pH 8.0 and modulate the functional activities of HMW
kininogen and
T-kininogen, degrading these
proteins at pH 8.0 or 4.5.