Reprint of: Comparison of the Chemical Properties of Selenocysteine and Selenocystine with Their Sulfur Analogs.

Some chemical properties of cystine and cysteine have been compared with those of their selenium-containing analogs. Major differences were noted between their titration curves, pK values of 2.01, 5.24, and 9.96 were observed for the ionizations of the carboxyl, selenohydryl, and amino groups, respectively, of selenocysteine. These values are compared with a pK of 2.3 for the carboxyl group of cysteine and values in the range of 8-10 for the ionization of the sulfhydryl and amino groups. Selenocysteine is much more reactive with halo acid derivatives than is cysteine, and reacts readily with iodoacetate even at pH values much below the pK of the selenohydryl group. Selenocysteine has an apparent half-wave potential of -0.212 V compared with 0.021 V for cysteine. It is unstable to acid hydrolysis, being completely decomposed by heating at 110° in 6 n HCl. It is also more soluble in water than is cysteine.

Platelet activating factors (AGEPC) from epidermal secretions of the Arabian Gulf catfish, Arius bilineatus, which stimulate wound healing.

High levels of platelet activating factor (PAF) activity were demonstrated by platelet aggregation and serotonin release assays to be present in fright induced epidermal secretions of the Arabian Gulf catfish, Arius bilineatus (Valenciennes, 1840). The PAF activity was purified by thin-layer chromatography. Mass spectral analysis combined with chemical and enzymatic modification of the purified PAF and inhibitor studies indicated that PAF activity was due to the presence of 1-O-alkyl-2-acetyl-sn-glycero-3-phosphorylcholine (AGEPC) molecules. The total AGEPC concentration in the epidermal secretions based on PAF assays was 8 x 10(8) M, well above the threshold level for platelet activation which is near 5 x 10(-11) M. Thus, stimulated epidermal secretory cells of Arius bilineatus supply platelet activating molecules at physiologically high concentrations to sites of injury.

Histopathological observations on organs from rabbits injected with the skin toxin of the Arabian Gulf catfish (Arius bilineatus, Valenciennes).

Toxicity of soluble protein extracts (skin toxin) from epidermal skin secretions of the catfish, Arius bilineatus (previously identified as Arius thalassinus), was examined in rabbits. Intravenous injections containing doses as low as 2 mg protein/kg body weight caused mortality in most animals tested. Histopathological examination of lung, heart, liver and kidney tissues of rabbits injected with skin toxin indicated that the lungs and livers of treated animals were adversely affected, while heart and kidney tissues appeared to be normal. Lethality of skin toxin was prevented by pretreatment of the rabbits with indomethacin. Histopathological examination of lung and liver tissues of indomethacin pretreated animals showed a significant reduction in the damage observed after injection of skin toxin.

Vasoconstrictor components in the Arabian Gulf catfish (Arius thalassinus, Ruppell) proteinaceous skin secretion.

The Arabian Gulf catfish (Arius thalassinus, Ruppell) produces toxic substances from its skin and from venom glands located near the base of the pectoral fins. Investigation of the pharmacological properties of the skin toxin have previously shown cholinergic vasoconstrictor activity in umbilical arteries. Cholinergic vasoconstriction was confirmed in sheep renal arteries. This activity was partially blocked by atropine, while most of the residual contraction was eliminated by simultaneous addition of indomethacin. Skin toxin treatment of arterial specimens caused a release of prostaglandin (PGE2, TXB2 and 6-keto-PGF1 alpha) into the organ bath. Prostaglandin release was blocked by pretreatment with indomethacin. Heat denaturation of skin toxin caused a loss of only the indomethacin-sensitive muscle contraction activity; most of the residual activity was blocked by atropine.

Pressure effects on metabolism in tissues from mice (Mus muscalis) and freshwater mussel (Elliptio complanata).

Metabolic rates of tissue sections from freshwater mussel gills and mouse brain and lung tissue were measured by calorimetry in ampules pressurized with gas mixtures. Increasing partial pressure of oxygen or total pressure with constant partial pressure of O2 does not affect the respiratory quotient but increases rates of tissue metabolism. Changes in metabolic activity occur over pressure and Po2 ranges commonly encountered by humans engaged in SCUBA diving.

Herbicide and estrogen effects on the metabolic activity of Elliptio complanata measured by calorespirometry.

Herbicides and estrogen are important contaminants of world water systems with effects on aquatic organisms. The effects of short-time exposure to atrazine, 2,4-Dichlorophenoxyacetic acid (2,4-D), paraquat, and estrogen on the metabolic activity of gill tissue from the freshwater bivalve Elliptio complanata were investigated by isothermal calorimetry and respirometry. Metabolic heat rates were altered following short-time exposure of gill tissue to these compounds over the concentration range from 10(-6) to 10(-3) M. The effects of herbicides and estrogen on metabolic heat rates were compound specific and time and concentration dependent. Treatment of tissue with estrogen caused stimulation of metabolic heat rates. In general, treatment with herbicides at low concentration or short times of exposure caused stimulation of metabolic heat rates, possibly due to uncoupling. Longer exposures and higher concentration subsequently caused inhibition of metabolic activity and decreased metabolic heat rates. Treatment of mitochondria isolated from gill and muscle tissues showed a similar pattern of respiratory rate stimulation at concentrations of 10(-4) M 2, 4-D and inhibition at higher concentration. Analysis of CO2 and O2 from the headspace gases in the calorimeter ampule showed an increase in the respiratory quotient indicating a shift in metabolism following addition of 2,4-D or paraquat.

F1-ATPase-catalyzed synthesis of ATP from oleoylphosphate and ADP.

Purified preparations of F1-ATPase (ATP phosphohydrolase; EC 3.6.1.3) isolated from yeast mitochondria catalyze the reaction of oleoylphosphate with ADP to yield ATP and oleic acid. Formation of ATP is specifically inhibited by the F1-ATPase inhibitor 1799 and by dinitrophenol. In the presence of F1, dinitrophenol "uncouples" the synthase reaction by causing rapid hydrolysis of oleoylphosphate without ATP formation. It is proposed that this F1 catalyzed ATP synthesis reaction corresponds to the terminal chemical step in oxidative phosphorylation.

Molecular and genetic events accompanying petite induction and recovery of respiratory competence induced by ethidium bromide.

The treatment of yeast cells with high levels of ethidium bromide causes a rapid induction of respiratory deficient mutants followed by a period of recovery to respiratory competence in 60 to 70% of the cells. Prolonged exposure then results in a final irreversible phase of petite formation. Sucrose gradient sedimentation analysis of 3H-adenine labelled mtDNA indicates that limited fragmentation (to about 16-18S) occurs during the initial phase of petite induction followed by a reassembly of the fragments during the period corresponding to the recovery of respiratory competence. The reassembly is associated with an ethidium bromide insensitive incorporation of 3H-adenine into mtDNA at a level consistent with repair synthesis. Genetic analyses, based on the transmission of five markers carried on the mtDNA of "repaired rho+" clones, suggests that reassembly occurs with a high degree of fidelity, though in two of a total of twenty five clones differences in marker transmission frequency were observed which could possibly reflect an altered gene order. In addition, a description is given of the marked changes in the suppressive nature of the treated cells and the temporary reduction in the capacity for marker transmission seen to accompany the transitory fragmentation of the mtDNA. The final phase of petite induction is an energy dependent degradation of the mtDNA to produce a rho degrees culture.

Metabolic response of Platynota stultana pupae during and after extended exposure to elevated CO(2) and reduced O(2) atmospheres.

The metabolic response of Platynota stultana pupae to elevated CO(2) and reduced O(2) atmospheres was measured using microcalorimetry. Initial measurements at 20 degrees C immediately upon placement in controlled atmosphere indicated a decrease in metabolic heat rate (MHR) of 27, 45, 56, 56, and 72% in an atmosphere of 5, 10, 20, 40, and 79% CO(2), respectively, and a decrease of 20, 50, 66 and 100% under 6, 2, 1, and 0% O(2). With extended exposure to controlled atmospheres, MHR increased under 5, 10, and 20% CO(2) and 6 and 2% O(2); however, the increase was greater and occurred more rapidly with lower CO(2) and higher O(2) concentration. The MHR at 40 and 79% CO(2) remained at the initial reduced level for 8 and 6 days, respectively, then decreased with longer exposure. The MHR of pupae held under 1 and 0% O(2) remained at the initial reduced level for 22 days. Upon transfer to air, the MHR of pupae increased from the reduced levels and then decreased. When the MHR decreased by no more than 30%, as a result of controlled atmosphere treatment, the pupae still developed into adults. However, when the MHR decreased by more than 50%, the energy supply was insufficient and the pupae died. Pupa mortality was comparable between 5% CO(2) and 6% O(2), and 10% CO(2) and 2% O(2). The MHR was reduced less under 20% CO(2) than under 2 or 1% O(2); however, the pupae were more susceptible to 20% CO(2) than 2 or 1% O(2). These and other data indicate an increased toxicity of high CO(2) over low O(2) atmospheres that may be related to an increase in membrane permeability as a result of CO(2) treatment.

DNA-dependent RNA polymerase from yeast mitochondria.

The DNA-dependent RNA polymerase present in the mitochondria of Saccharomyces cerevisiae has been solubilized using a 0.5 M KCI solution, and the soluble enzyme has been purified. Two forms of mitochondrial enzyme were obtained; they differ in their template specificity and metal-ion dependency. The mitochondrial RNA polymerase also differs from enzyme obtained from the nucleus with respect to antibiotic sensitivity and template specificity. Only the nuclear enzyme is sensitive to alpha-amanitin inhibition. The relative activities of the isolated nuclear and mitochondrial polymerases toward their homologous DNAs are consistent with their in vivo functions. The possibilities of bacterial- and nuclear-enzyme contamination of the mitochondrial enzyme preparation have been ruled out. RNA polymerase activity in two petite mutants has been studied. Isolated mitochondria from a petite mutant with no detectable mitochondrial DNA has greatly diminished mitochondrial DNA-dependent RNA polymerase activity, while a petite mutant with only a small change in mitochondrial DNA base composition has normal amounts of enzyme.

Characterization of deoxyribonucleic Acid species from castor bean endosperm: inability to detect a unique deoxyribonucleic Acid species associated with glyoxysomes.

Three DNA buoyant density species (nuclear, 1.692 g cm(-3); mitochondria 1.705 g cm(-3); and proplastid, 1.713 g cm(-3)) can be detected in extracts from castor bean endosperm. No other buoyant density species can be identified. DNA extracts from sucrose density gradient purified glyoxysomes exhibit varying amounts of each of the three identified DNAs but no other distinguishable DNA species. RNA synthesized in vitro by Escherichia coli RNA polymerase using purified castor bean nuclear DNA as a template, hybridizes equally well with its template and with the 1.692 g cm(-3) species from glyoxysome fractions. These results are discussed in terms of their relevance to microbody biogenesis.