Synthesis of porphyrins by cell suspensions of Tetrahymena vorax: effect of members of the vitamin B group

Phenotype switching in polymorphic Tetrahymena: a single-cell Jekyll and Hyde

For nearly half a century, phenotype switching in the group of polymorphic species of the ciliate genus Tetrahymena has been the subject of investigations of the underlying mechanisms, the accompanying biochemical and structural changes, and the evolution of polymorphic survival strategy. Beginning with the pioneering systematic studies by Furgason in 1940 of hymenostome ciliates, the experimental approach rapidly expanded to include investigations of growth, nutrition, physiology, morphology, and morphogenesis in the polymorphic species. Recently, with progress in elucidation of the novel signaling ligand and identification of elements of the subsequent signal transduction cascade, in addition to the growing catalog of intracellular events associated with differentiation in these unicellular eukaryotes, we have begun to address the mechanistic basis of polymorphism. This review summarizes and integrates the history and recent discoveries concerning Tetrahymena polymorphic cells. We are now poised to answer fundamental questions about this interesting pathway of cell differentiation.

Isolation and characterization of a new mutant of Saccharomyces cerevisiae with altered synthesis of 5-aminolevulinic acid

A new gene, RHM1, required for normal production of 5-aminolevulinic acid by Saccharomyces cerevisiae, was identified by a novel screening method. Ethyl methanesulfonate treatment of a fluorescent porphyric strain bearing the pop3-1 mutation produced nonfluorescent or weakly fluorescent mutants with defects in early stages of tetrapyrrole biosynthesis. Class I mutants defective in synthesis of 5-aminolevulinate regained fluorescence when grown on medium supplemented with 5-aminolevulinate, whereas class II mutants altered in later biosynthetic steps did not. Among six recessive class I mutants, at least three complementation groups were found. One mutant contained an allele of HEM1, the structural gene for 5-aminolevulinate synthase, and two mutants contained alleles of the regulatory gene CYC4. The remaining mutants contained genes complementary to both hem1 and cyc4. Mutant strain DA3-RS3/68 contained mutant gene rhm1, which segregated independently of hem1 and cyc4 during meiosis. 5-Aminolevulinate synthase activity of the rhm1 mutant was 35 to 40% of that of the parental pop3-1 strain, whereas intracellular 5-aminolevulinate concentration was only 3 to 4% of the parental value. Transformation of an rhm1 strain with a multicopy plasmid containing the cloned HEM1 gene restored normal levels of 5-aminolevulinate synthase activity, but intracellular 5-aminolevulinate was increased to only 9 to 10% of normal. We concluded that RHM1 could control either targeting of 5-aminolevulinate synthase to the mitochondrial matrix or the activity of the enzyme in vivo.

Growth cycle-dependent overproduction and accumulation of protoporphyrin IX in Tetrahymena: effect of heavy metals

Cells of the ciliate Tetrahymena pyriformis GL overproduce and accumulate massive quantities of the heme intermediate, protoporphyrin IX. Protoporphyrin is localized intracellularly in discrete membranous compartments. The amount of porphyrin stored in the cell changes dramatically as cells progress through the growth cycle. Porphyrin overproduction is stimulated by delta-aminolevulinic acid, but only during the mid-stationary phase. Overproduction of protoporphyrin IX apparently results from an increase, late in the growth cycle, of activities subsequent to delta-aminolevulinic acid synthetase. Feedback inhibition in the pathway by accumulated protoporphyrin IX does not occur. The presence of Co2+ completely inhibits accumulation of protoporphyrin IX in a manner reversed by delta-aminolevulinic acid. Sn4+ stimulates protoporphyrin IX accumulation in the culture.

Urinary excretion of porphyrins in two cases of porphyria cutanea tarda during a period of various treatments

The urinary excretion of porphyrins in two cases of porphyria cutanea tarda (PCT) has been followed during a period in which various treatments have been tried. In one patient pyridoxal-5-phosphate (P-5-P) injections lead to a dramatic increase in porphyrin excretion. In another P-5-P treatment was followed by a significant decrease in porphyrin excretion. p-Aminobenzoic acid (PABA) apparently had no effect on porphyrin excretion, while repeated phlebotomies had the expected effect. In both patients all variations in the total amount of porphyrins excreted were almost exclusively due to the variations in the amounts of heptacarboxylic porphyrin type III and uroporphyrin I. A secondary finding was an increase in hexa- and penta-carboxylic porphyrins type III without a concomitant increase in coproporphyrin III.

Coproporphyrinogenase in tobacco (Nicotiana tabacum L.)

1. Coproporphyrinogenase was extracted and purified from tobacco (Nicotiana tabacum L.). Enzyme activity was mainly located in mitochondria rather than in chloroplasts. The enzyme was purified by differential centrifugation, ammonium sulphate fractionation, calcium phosphate gel adsorption and dialysis. A 69-fold final purification was obtained. 2. An apparent K(m) value of 3.6x10(-5)m was found, the value being largely dependent on the amount of coproporphyrin III recovered after reduction with sodium amalgam to coproporphyrinogen III. Protoporphyrin formation was linear up to 3h and decreased with further incubation. The enzyme activity increased with the concentration of enzyme protein up to 30mug/ml of solution. 3. Enzyme activity was greatly enhanced by increasing Fe(2+) concentrations up to 0.5mm, beyond which inhibition occurred. Co(2+) and Mn(2+) were also found to activate at low concentrations (0.1mm) and inhibit at higher concentrations (5mm). Fe(3+) and Cu(2+), both at 0.1mm, and o-phenanthroline and EDTA, each at 1mm, were found to be inhibitory.