Morris Lieberman

Ethane Evolution: A New Index of Lipid Peroxidation

Homogenates of mouse liver and brain at 37�C spontaneously formed lipid peroxides and simultaneously evolved ethane. α-Tocopherol, a lipid antioxidant, blocked ethane formation. When mice were injected with carbon tetrachloride (a liquid prooxidant for liver), the animals produced ethane. Ethane evolution in vivo was stimulated by prior administration of phenobarbital and it was diminished by prior injection of α-tocopherol. These data suggest that ethane production may be a useful index of lipid peroxidation in tissue homogenates and in intact animals.

Induction of ethylene biosynthesis in tobacco leaf discs by cell wall digesting enzymes

Abstract Cellulysin induces ethylene production in tobacco leaf discs by initiating the formation of 1-aminocyclopropane-1-carboxylic acid. Induction occurred within 30 to 60 min of incubation and was inhibited by aminoethoxyvinylglycine, and the antiproteases, PMSF and soybean trypsin inhibitor. Cycloheximide (CHI) at 2.8 μg/ml and chloramphenicol (CAP) at 100 μg/ml did not inhibit this induction although incorporation of the label from (3,4- 14 C)methionine into the acid-insoluble fraction was inhibited by 57%. At 14 μg/ml CHI, and CAP, ethylene production was inhibited by 25% while protein synthesis was inhibited by 75%. We suggest that either the low amounts of protein synthesis that appear to be insensitive to CHI is sufficient to induce ethylene biosynthesis or that Cellulysin activates a preexisting but inactive form of ACC synthase to promote ethylene biosynthesis. Also, induction of ethylene production by microbial enzymes that digests plant cell walls may be an initial protective response of plants that serves to combat microbial infection.

Ethylene Formation in Rat Liver Microsomes

Reduced triphosphopyridine nucleotide and pyrophosphate-dependent peroxidation of lipids in rat liver microsomes were coupled to the generation of ethylene in the presence of cuprous ions. This system suggests a model for the biogenesis of ethylene in cells.

Thoughts on the Role of Ethylene in Plant Growth and Development

Of all the regulator substances which influence physiological development of plants ethylene stands apart in its wide-ranging effects on most aspects of growth and development. Table I is a partial list of some responses caused by ethylene. These responses vary from stimulation of seed germination (Vacha and Harvey, 1927), retardation of seedling growth (Knight and Crocker, 1913), induction of flower formation (Traub et al, 1940), to acceleration of senescence (Biale et al, 1954). The marked effect of ethylene is therefore not only observed in fruit ripening, its traditional role, but also in vegetative and reproductive metabolism. Ethylene appears to exert an influence on all aspects of metabolism, throughout the life-cycle of the plant.

Inhibition of 1-Aminocyclopropane-1-Carboxylic Acid Synthase by Phenothiazines*

Summary Trifluoperazine (TFP), chlorpromazine (CPZ) and CPZ analogs, the phenothiazine drugs which are antagonists of calmodulin, inhibit tomato fruit 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity. The I50 dose ranged between 20 μM and 58 μM for various analogs. Inhibition was not influenced by light or by varying the calcium concentration. CPZ caused a hyperbolic uncompetitive type of inhibition. The enzyme showed a high affinity for long chain alkyl and ω-aminoalkyl agarose hydrophobic columns. However, the enzyme was not retained on QAE Sephadex or calmodulin-Sepharose columns which, under standard conditions, are known to bind calmodulin. Thus, although the phenothiazines inhibit ACC synthase, the mechanism probably does not involve calmodulin; rather, the inhibition may occur through fortuitous hydrophobic interactions of inhibitor and enzyme.

Variations in Adenylates and Adenylate Energy Charge During Phosphate-mediated Inhibition of Ethylene Biosynthesis in Penicillium digitatum

Summary Changes in adenine nucleotides and adenylate energy charge in shake cultures of Penicillium digitatum were determined under conditions when ethylene biosynthesis was either activated or inhibited. Activation of ethylene biosynthesis under phosphate-limiting growth conditions was accompanied by a 28% decrease in the ATP level of the mycelia. Under these growth conditions, changes in the adenylate energy charge were inversely related to the concentration of AMP but did not correlate with changes in the rate of ethylene biosynthesis or in total adenylate nucleotides. Adenine and AMP, when added individually, partially prevented the inhibitory effect of 0.01 mM orthophosphate on ethylene biosynthesis. On addition of orthophosphate, orthophosphate and adenine, or orthophosphate and AMP a rapid decrease within 2 hours in ethylene biosynthesis occurred without a striking increase in the ATP level of the cultures. In non-growing mycelia of P. digitatum , there was considerable modulation in the concentration of individual adenine nucleotides but only small changes in the adenylate energy charge were observed. The data indicated that levels of adenylates, glutamate, or the adenylate energy charge do not mediate or limit phosphate inhibition of ethylene biosynthesis. However, it is suggested that an orthophosphate-repressible phosphatase and/or a protein kinase may be involved in this process.