Phosphoenolpyruvate Carboxylase fromMesembryanthemum crystallinum: Its Isolation and Inactivationin vitro

Abstract

Phosphoenolpyruvate carboxylase (PEPC) was isolated from leaves of Mesembryanthemum crystallinum, which performed Crassulacean acid metabolism. PEPC was much more stable when extracted from expanded than from expanding leaves. The inactivation of PEPC in desalted extracts from expanding leaves was much faster at 25 than at 0 °C, was stimulated by raising Mg²⁺ from 0.1 to 3.0 mM, and was reduced by bovine serum albumin. The same type of inactivation was found after mixing extracts from the two types of leaves, and the decrease in PEPC activity then also included inactivation of the ’stable’ PEPC from the expanded leaves. After elution from DEAE-cellulose, PEPC from expanding leaves was much more stable than in desalted, crude extracts. It is suggested that another enzyme is involved in this inactivation of PEPC, but this needs verification.