Calcium-dependent properties of peptidylarginine deiminase from rabbit skeletal muscle.

Abstract

Peptidylarginine deiminase, which catalyzes the deimination of arginyl residues in protein, required Ca2+ as an essential cofactor and the half-maximal activity was attained at 40—60 μm Ca2+. Other divalent cations were practically inactive except for Sr2+, which was about 50% as active as Ca2+ when tested at 10 mm. However, Sr2+ at less than the concentration of 100 μm had little or no activity. The direct Ca2+-binding for the enzyme showed a sigmoidal curve with a transition midpoint of about 110 μm, indicating that the binding is cooperative. Analysis of Hill plots of the data revealed that the enzyme binds 3 mol of Ca2+/mol of protein with an apparent dissociation constant of llO μm. A conformational change upon Ca2+-binding was also described for the enzyme using UV-difference spectra. The alteration could be attributed to an increased exposure of the aromatic residues to a more aqueous environment, as has been described for Ca2+-binding proteins such as calmodulin. Phosphatidylserine enhanced the re...