Purification, molecular and enzymic characterization of an acid RNase from the insect Ceratitis capitata

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  • Definition. Fick, unit of diffusion equivalent to 10−7 cm2· s−1.

  • Note. Portions of this paper (including Materials and Methods, Tables 1 and 3, and Figs 1, 5, 6 and 7) are presented in miniprint at the end of the paper.

Correspondence to J. M. García-Segura, Departamento de Bioquimica, Facultad de Ciencias Quimicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain

Abstract

An acid ribonuclease has been purified from the insect Ceratitis capitata. The specific activity of the purified enzyme is 580 units/mg. This enzyme is a single polypeptide chain of about 35.5 kDa, containing only one disulfide bridge and no free – SH groups. The A0.1%1 cm at 280 nm is 1.90. The hydrodynamic radius of the native enzyme is 2.5 nm. The secondary structure of this RNase is composed of 10%α-helix, 31%β-structure and 59% aperiodic conformation with an average number of residues per helical segment of 10, based on circular dichroic measurements. Optimum parameters for the enzyme activity are pH 5.5, 0.15 M ionic strength and 40°C. Divalent cations are not required for the enzymic catalysis. This enzyme has been characterized as cyclizing endoribonuclease.

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