Rhodanese functions as sulfur supplier for key enzymes in sulfur energy metabolism

How microorganisms obtain energy is a challenging topic, and there have been numerous studies on the mechanisms involved. Here, we focus on the energy substrate traffic in the hyperthermophilic bacterium Aquifex aeolicus. This bacterium can use insoluble sulfur as an energy substrate and has an intricate sulfur energy metabolism involving several sulfur-reducing and -oxidizing supercomplexes and enzymes. We demonstrate that the cytoplasmic rhodanese SbdP participates in this sulfur energy metabolism. Rhodaneses are a widespread family of proteins known to transfer sulfur atoms. We show that SbdP has also some unusual characteristics compared with other rhodaneses; it can load a long sulfur chain, and it can interact with more than one partner. Its partners (sulfur reductase and sulfur oxygenase reductase) are key enzymes of the sulfur energy metabolism of A. aeolicus and share the capacity to use long sulfur chains as substrate. We demonstrate a positive effect of SbdP, once loaded with sulfur chains, on sulfur reductase activity, most likely by optimizing substrate uptake. Taken together, these results lead us to propose a physiological role for SbdP as a carrier and sulfur chain donor to these key enzymes, therefore enabling channeling of sulfur substrate in the cell as well as greater efficiency of the sulfur energy metabolism of A. aeolicus.     

Seasonal change and sex difference in drug-metabolizing activity in frog liver microsomes

The drug-metabolizing activities (aminopyrine N-demethylase and p-nitroanisole O-demethylase activities) have been measured at monthly intervals throughout the year in liver microsomes of male and female Japanese bullfrogs, Rana catesbeiana. The aminopyrine N-demethylase activity based on cytochrome P-450 of both sexes was significantly higher in May-July (spring-summer) than in August-October (summer-autumn). On the contrary, the p-nitroanisole O-demethylase activity based on cytochrome P-450 of males was significantly higher in July-October (summer-autumn) than in May-June (spring). However, there was no seasonal changes in the O-demethylase activity in females. There were significant differences between males and females in the N-demethylase activity in August-October and in the O-demethylase activity in May-June (or July-October).     

Sulfurtransferases and the content of cysteine, glutathione and sulfane sulfur in tissues of the frog Rana temporaria

L-cysteine desulfuration was examined in tissues of Rana temporaria, in October and January. The activities of 3-mercaptopyruvate sulfurtransferase (MPST), cystathionine gamma-lyase (CST) and rhodanese were primarily concentrated in frog liver and kidney. The values of CST and rhodanese activity, as well as sulfane sulfur compounds levels fell in the range characteristic of rat. For each of the investigated tissues changes noted in the enzymatic activities and in the level of glutathione (GSH), protein-bound cysteine (PbCys) and sulfane sulfur compounds were dependent on the month in which the determination was performed, and on the character of the tissue. In such tissues as the liver or gonads, high GSH levels and high activities of MPST (in the liver) or MPST and rhodanese (in the gonads) seemed to accompany protein biosynthesis during hibernation. PbCys, the level of which was consequently diminished in all tissues in January, compensated the absence of exogenous cysteine. A significantly reduced GSH level in the brain in January seemed to be correlated with decreased requirements of the tissue for this important natural antioxidant at diminished thyroid hormones levels in the serum and minimal oxygen consumption during the hibernation. In the kidney, the possible participation of sulfane sulfur compounds in detoxification processes requires elucidation, similarly as in protection against cellular oxidative stress at extremely low levels of GSH.     

Increased proliferative activity in selenium-deficient mouse liver

Male albino NMRI mice were fed a selenium-deficient (Se-), torula yeast-based diet containing less than 10 ppb Se for at least 2 months (Se-) while a control group received the same diet supplemented (Se+) with 330 ppb Se as Na2SeO3. The Se-(-)animals showed multiple enzyme modulations of liver enzyme activities indicating that they were in a severely Se- state. No significant difference in the basic DNA synthesis rate of Se-(-)animals compared to Se+ controls was measured. However, when liver cell proliferation was induced by either hepatopoietin pretreatment or by partial hepatectomy, an about 3-fold increase in DNA replication rates was found in Se- compared to controls. We conclude that the enhanced proliferative activity in Se- mouse liver is expressed in an emergency situation.     

Disulfide reductase activity in mouse regenerating liver

Fourteen hours after partial hepatectomy there was a decrease in basal disulfide reductase and glutathione reductase activity in cytosole fraction of proliferating hepatocytes. In nuclear fraction, the activation effect of cAMP and cGMP on the disulfide recovery was replaced by inhibition. Meanwhile the activity of glutathione reductase noticeably increased. Forty-five hours after operation disulfide reductase activity of cytosole appreciably rose during maximal mitotic activity of the regenerating liver. The data obtained provide evidence in favor of the involvement of disulfide reductase enzymes into reparative regeneration of the liver.     

Purification and characterization of mouse alcohol dehydrogenase from two inbred strains that differ in total liver enzyme activity

Alcohol dehydrogenase activity in mouse liver homogenate-supernatants is 1.7 times greater in the C57BL/10 strain than in the BALB/c strain, regardless of whether activity is expressed in units per gram liver, total liver, or milligram DNA. The K _m values for ethanol and NAD⁺, approximately 0.4 and 0.03mm, respectively, of enzyme purified from both strains are similar. Moreover, the K _i for NADH, 1 µm, the pH optimum for ethanol oxidation, 10.5, and the V _max for ethanol oxidation, 160 min^–1, for ADH from the C57BL/10 and BALB/c strains are similar. Therefore, the difference in ADH activity in the two strains cannot be due to differences in the catalytic properties of the enzyme. The electrophoretic and isoelectric focusing patterns and two-dimensional tryptic peptide maps of the purified enzyme from both strains are identical. Thus the amino acid sequences of enzyme from C57BL/10 and BALB/c mice must also be identical or very similar. The difference in ADH activity in the two strains is most likely the result of genetic differences in the content of ADH protein in liver.Supported by NIAAA Grant AA 04307.     

Seasonal change and sex difference in laurate hydroxylase activity in frog liver microsomes

The content of cytochrome P-450 and the specific activity of laurate hydroxylation have been measured at monthly intervals through the year in liver microsomes of males and females of Japanese bullfrog, Rana catesbeiana. The specific activity, based on microsomal protein or cytochrome P-450 of both sexes was higher in spring (April-May) than in autumn (October-November) and the difference was statistically significant. However, in males the content of the cytochrome P-450 in the spring was almost the same level as in the autumn and it was rather lower in the spring than in the autumn in females. These suggest that the cytochrome P-450 species catalyzing laurate hydroxylation increased specifically in the spring. The specific activity (based on cytochrome P-450) in males was significantly higher than that in females in spring (April-May) or autumn (October-November).     

Rhodanese and ALA-S in mammary tumor and liver from normal and tumor-bearing mice.

1. Basal levels and allyl-isopropylacetamide (AIA) or veronal induced levels of delta-amino-levulinate synthetase (ALA-S), cytoplasmic and mitochondrial rhodanese were determined in tumor (T) and liver of both normal mice (NM) and T-bearing mice (TBM). 2. Rhodanese tumoral mitochondrial levels were higher than the hepatic normal mitochondrial fraction, while the cytoplasmic activity was nearly equal in all sources. 3. In neither case was the activity of tumoral ALA-S and rhodanese altered by any of the porphyrinogenic drugs. 4. Mitochondrial and cytoplasmic rhodanese activity was also measured in tumor and liver of TBM at different intervals after transplantation. We concluded that the behaviour of rhodanese is a property inherent to the tissue and not one attained with time.     

Tyrosine aminotransferase activity of frog (Rana esculenta) liver

1. The presence of tyrosine aminotransferase is reported both in particulate and soluble fractions of frog liver. 2. The activity of the soluble enzyme of frog liver was investigated with regard to its dose and time dependence, its substrate specificity and concentration dependence, its thermal sensitivity as well as pH and temperature dependence. 3. It appears that the properties of the soluble tyrosine aminotransferase of frog liver are in close agreement with those reported for the mammalian liver enzyme.     

Enhanced prenyltransferase activity and Rab content in rat liver regeneration

Rabs are small GTP-binding proteins with a regulatory role in intracellular vesicular traffic. The modulation of their levels and activity in different physiological situations is poorly understood. During the first cell cycle of rat liver regeneration we observed a differential regulation of some Rabs, with a progressive increase of those involved in exocytosis and a progressive decrease of one involved in endocytosis. This could be related with the need of exposing growth factor receptors and prolonging the transduction of their signal in preparation for mitosis. Moreover, we observed an increased activity of protein prenyltransferases, the enzymes responsible for the prenylation of several proteins involved in crucial processes of proliferation, without a corresponding increase in the amount of prenyltransferase protein.     

Circannual rhythm of the melanin content in frog liver (Rana esculenta L.)

The melanin content of Rana esculenta L. liver varies according to a circannual statistically significant rhythm, as shown by variance and single cosinor analysis. The maximum is found in autumn-winter, the minimum in spring-summer. The linear regression analysis shown a negative correlation between the amount of melanin and the environmental temperature.     

Phagocytic activity in mouse embryonic liver and spleen following hemolysis

Phenylhydrazine (PHZ) was injected into pregnant mice and the number of phagocytizing cells was counted in the embryonic livers and spleens at 11th to 14th gestational days. A marked increase in the number of phagocytizing cells was observed in the embryonic spleen, whereas in the embryonic liver it was only slightly enhanced. This observation indicates that the response to hemolytic events is similar in embryonic and adult mammals.