Purification and properties of a ribonuclease from cowpea cotyledons

The isolation and characterisation of cotyledonary ribonucleases (RNase; EC 3.1.27.1), are basic steps to understand the physiology and biochemistry of RNA turnover and mobilisation during seed germination and seedling establishment, as well as how environmental stresses affect them. RNase was isolated and purified 928-fold, to apparent eletrophoretic homogeneity from 5-d-old seedlings of Vigna unguiculata. It is a protein with an apparent molecular mass of 16 kDa having three major isoforms. Its optimum pH is 5.8, which decreases to 5.2 in presence of KCl, It has an apparent K-m of 0.80 mg RNA cm(-3) and retains 40 % of its activity when heated to 80 degrees C, It is completely inhibited by Cu2+, Hg2+ and Zn2+ and is almost insensitive to Mg2+, Ca2+ and EDTA, Urea, Fe2+, Co2+ and 2-mercaptoethanol partially inhibit its activity. Its amino acid composition shows a resemblance to that of other plant RNases.