Vitamin K-dependent carboxylase. Control of enzyme activity by the "propeptide" region of factor X |
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Authors: | J E Knobloch J W Suttie |
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Institution: | Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison 53706. |
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Abstract: | A liver microsomal enzyme catalyzes the vitamin K-dependent posttranslational carboxylation of specific glutamyl residues of a limited number of plasma proteins to gamma-carboxyglutamyl residues. The intracellular precursor forms of these proteins are known to contain a homologous basic amino acid-rich propeptide region between the signal peptide region and the amino terminus of the mature protein. This region of the precursor protein has been implicated as a possible recognition site for the carboxylase enzyme. A 20-residue peptide containing the octadecapropeptide of human clotting factor X has now been shown to strongly stimulate the activity of the enzyme toward a noncovalently linked substrate. This stimulatory effect is seen at less than micromolar concentrations and is accompanied by a decrease in the Km of the glutamic acid substrate. These observations raise the possibility that the catalytic activity of other enzymes involved in protein processing may be regulated by a portion of their normal substrates. |
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