A novel proteinase and its specific protein-inhibitor in Spinacia oleracea leaf

A novel proteinase has been evidenced in spinach (Spinacia oleracea L.) leaves. Substrate and inhibitor specificities of the purified enzyme indicate that this proteinase is different from the previously described proteinase which displays a peculiar leucine specificity. A proteinase protein-inhibitor has been evidenced in the same extract, along with the already described anti-trypsin inhibitor. This novel protein-inhibitor has no activity against trypsin while it is effective against the proteinase described here. Furthermore, the observed inhibition shows ionic strength dependence, a characteristic common to many plant proteinase/specific inhibitor systems.