Differential Effect of Phosphate Starvation on the Rates of Cell Division and Plastid Replication in Euglena*

SYNOPSIS. The effects of phosphate starvation on the synthetic and division rates of Euglena gracilis strain Z are described. Phosphate starvation inhibits rates of the following processes, in the order: RNA synthesis > DNA synthesis > cell division > chlorophyll synthesis and plastid replication. As a consequence of the differential effect of phosphate starvation on the synthetic and division rates the average gross chemical composition of the cells is subject to continuous change.     

Tissue culture studies. V. Analogues for nicotinic acid

The use of acetyl-3-pyridine and pyridine-3-sulfonic acid as analogues for nicotinic acid has been tested with tissue cultures of embryonic chick heart. Both roller tube and Carrel flask cultures were employed. Cell migration, appearance of the cells, and the uptake of tracer P³² were used as criteria for the action of the analogues. Migration of the cells could be inhibited by both compounds, but at different levels. Both produced abnormal types of cells, but not the same type of abnormality. Uptake of P³² was inhibited by both compounds. Addition of nicotinic acid failed to reverse the effects of the analogues at the concentrations used.     

Pheomelanin Production by the Lipoxygenase-Catalyzed Oxidation of 5-S-Cysteinyldopa and 5-S-Cysteinyldopamine

5-S-cysteinyl-dopa (cysdopa) and 5-S-cysteinyl-dopamine (cysdopamine) are oxidized in vitro by soybean lipoxygenase (LOX) in the presence of hydrogen peroxide giving rise to the corresponding pheomelanins. The reaction is activated by caffeic acid and other catechols, suggesting a cofactor role for these compounds. The activating effect is proportional to the concentration of the cofactor, with a saturation profile. The activation extent of the various cofactors is directly related to LOX affinity for the same compounds. The possible implications of the peroxidative action of LOX in Parkinson's disease and in aging are discussed.     

Production of Melanins by Ceruloplasmin

It was shown that ceruloplasmin, apart from the known oxidative conversion of dopamine into melanin, can also produce (DHI)-melanin from 5,6-dihydroxyindole and THP-melanin from tetrahydropapaveroline. Ceruloplasmin acts as an oxidase and the kinetic parameters for these oxidative reactions are reported. Since these ceruloplasmin-catalyzed reactions occur also at pH 7.4, they could have a significant physiological impact. This ceruloplasmin-oxidasic activity is enhanced by copper ions and inhibited by chelators, such as ethylenediaminetetraacetic acid (EDTA) and desferoxamine (DEF). Some possible implication of melanin production in blood are discussed.