The demonstration that the reactions of fl oxidation and the glyoxylate cycle occur in the glyoxysome, a cellular organelle isolated from castor bean endosperm, has raised the question of the intracellular location of the enzymatic activation of free fatty acids in this tissue. Glyoxysomes, isolated on sucrose gradients, have been shown to contain a thiokinase which, in the presence of CoA, MgC...

Membrane deterioration in plant senescence is commonly associated with progressive decreases in membrane phospholipid content. This study investigated the expression and regulation of phospholipase D (PLD; EC 3.1.4.4) during senescence in castor bean (Ricinus communis L. cv Hale) leaf discs. The rate of leaf senescence was accelerated by 50 [mu]M abscisic acid and was attenuated by 50 [mu]M cyt...

Cytosolic pyruvate kinase from endosperm of germinating castor beans (Ricinus communis L.; cv Hale) has been purified 3100-fold to apparent homogeneity and a final specific activity of 203 micromole pyruvate produced/minute per milligram protein. Purification steps included: heat treatment, polyethylene glycol fractionation, Q-Sepharose, ADP-agarose, Mono-Q and Phenyl Superose chromatography. N...

A base exchange reaction for synthesis of phosphatidylethanolamine by the endoplasmic reticulum of castor bean (Ricinus comminus L. var Hale) endosperm has been examined. The calculated Michaelis-Menten constant of the enzyme for ethanolamine was 5 micromolar and the optimal pH was 7.8 in the presence of 2 millimolar CaCl(2). l-Serine, N-methylethanolamine and N,N-dimethylethanolamine all reduc...

Crude particulate preparations from castor bean endosperm contain most of the /3 oxidation activity present in initial extracts. Measurements on organelles separated by sucrose density centrifugation of the crude particles show that glyoxysomes (density 1.25) contain more than 80% of the particulate /3 oxidation activity, with virtually none in the mitochondria (density 1.19). Thiolase shows a ...