Structural and Functional Characteristics of Ribulose-1,5-Bisphosphate Carboxylase from Spirulina platensis

Abstract

Optimization of protein extraction for food use by wet fractionation procedure requires knowledge of the possible degradation processes which usually accompany the purification procedures and of the basic molecular features of the particular protein. Proteolytic degradation of ribulose-1,5-bisphosphate carboxylase (RuBPcase) observed in crude extracts of Spirulina platensiswas partially inhibited by the addition of phenyl-methyl-sulphonyl-fluoride as a proteinase inhibitor. The RuBPcase purified to electrophoretic homogeneity by a laboratory method was characterized for molecular weight, isoelectric point, solubility as a function of pH and ionic strength, and heat stability. Since degradation of purified plant RuBPcase is related to the redox state of enzyme thiol groups we have investigated the relationship between the number of oxidized thiol groups and the residual activity in the purified preparation of RuBPcase from Spirulina platensis. Furthermore, the susceptibility of the enzyme to various transition metals, able to catalyse the oxidation of thiol groups, was evaluated and the functional role of thiol groups for the maintenance of the native structure of RuBPcase is discussed. The results obtained are presented and discussed in view of the potential industrial extraction of RuBPcase from Spirulina platensis.