JBC, Vol. 250, Issue 3, 843-847, Feb, 1975
The interaction of inhibitors of proteolytic enzymes with 3-methylhistidine-57-chymotrypsin
D. S. Ryan and R. E. Feeney
The inhibition of proteolytic enzymes by protein inhibitors is accompanied
by the formation of unusually stable complexes. The recognition of a
specific substrate-like amino acid on the inhibitor is believed to be the
initial event of the inhibitory process. In addition to the interactions
involved in the binding of a good substrate, a variety of other noncovalent
interactions are known to stabilize the complex. The formation of stable
complexes between several inactive derivatives of proteolytic enzymes and a
variety of protein inhibitors suggests strongly that the formation of any
species resembling catalytic intermediates is unnecessary for inhibition.
We have examined the interaction between several avian ovomucoids and
alpha-chymotrypsin in which histidine-57 has been converted to
3-methylhistidine-57. This derivative is easily prepared and can be
isolated by affinity chromatography. Methylchymotrypsin retains unaltered
its ability to bind specific substrates, but is essentially inactive. In
spite of this loss of enzymatic activity, methylchymotrypsin forms strong
complexes with several inhibitors. In addition, methylchymotrypsin which
has been covalently linked to Sepharose is particularly useful for the
isolation of protein inhibitors without the complications due to isolation
of a mixture of partially cleaved forms of the inhibitor.
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