Uptake of Na275SeO3 by mitochondria of the larvae of the insect C. cephalonica reared at different dietary selenium (Se) levels revealed: 1. A proportional increase in the uptake with externally added Na275SeO3 in concentrations upto 25.32 μM; and 2. At each added selenite concentration, an increase up to 60 min, with linearity up to 15-30 min. A differential affinity for Na275SeO3 was elicited in the mitochondrial protein fractions of different dietary Se groups and correlated well with the pattern and the ratio of distribution of incorporated75Se in protein to nonprotein fractions. Kinetic studies on75Se uptake by whole mitochondria negated passive diffusion of selenite and revealed a trend of negative cooperativity confirmed by Hill and Scatchard plots. Half saturation value was estimated to be approx 13 nmole Se/mg mitochondrial protein. Scatchard plot for75Se uptake was biphasic and the high affinity binding sites were estimated to be around 5 nmole/mg mitochondrial protein. Calculated dissociation constants revealed maximal affinity for75Se in the 1.5 ppm group (KSe 0.0034 n M) and minimal in the basal group (KSe 0.007 n M). In the mitochondria of all the three dietary Se groups, the estimated low affinity sites amounted to be 15-19 nmole/mg mitochondrial protein. Inherent Se in the mitochondria of the high Se group positively enhanced the incorporation of75Se in the mitochondrial protein fraction. About 20-30% of the total uptake was indicated to be energy linked as revealed by studies with respiratory inhibitors. Addition of sulfite and sulfate (5-25 μM) in the medium, inhibited75Se uptake by 35-55%, suggestive of the involvement of the dicarboxylate port. Thiol interactive75Se uptake was confirmed by the inhibition mediated by mersalyl and NEM up to 50-70%. The study revealed thiol-selenite interactions of metabolic significance during selenite uptake. © 1995 Humana Press Inc.

Kalyanaraman Lalitha

selenite

selenium

animal tissue

article

controlled study

insect

INTRACELLULAR TRANSPORT

Larva

Membrane transport

Mitochondrion

nonhuman

transport kinetics

Animal

ETHYLMALEIMIDE

INSECTS

Kinetics

MERSALYL

Mitochondria

oxygen consumption

Proteins

SELENIUM RADIOISOTOPES

Succinates

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Mitochondrial selenium-75 uptake and regulation revealed by kinetic analysis.

Biological Trace Element Research

Uptake of (75Se) added in vitro was followed in mitochondria isolated from Trigonella foenum-graecum seedlings grown under different Se status (0.5-1.0 ppm) and with added mimosine (0.1 mM). Uptake of 75Se followed with added Na2 75SeO3 up to 20 μM in the medium was nonlinear in all the groups. Kinetic analyses of the uptake of 75Se for 1 min were carried out for ali the groups. The results indicated a cooperative effect during Se transport. Graphical analyses using the Hill plot and Scatchard plot confirmed the existence of negative cooperativity during 75Se uptake. Scatchard plots were biphasic, suggesting the probable presence of two classes of binding sites. The presence of succinate or ATP in the incubation medium inhibited 75Se uptake by 40%. Studies with mitochondrial respiratory inhibitors indicated the uptake to be energy independent. A decrease in the uptake of 75Se by 40% effected by HgCl2, N-ethyl maleimide, and iodoacetate confirmed the interaction of active thiols in the process. The present study confirms the controlled nature of 75Se uptake by plant mitochondria.

Kinetic analyses of mitochondrial 75selenium uptake in Trigonella foenum-graecum seedlings exposed to selenium and mimosine

Mitochondrial selenium-75 uptake and regulation revealed by kinetic analysis

Requirement, uptake, and subcellular distribution of Na275SeO3 in the larvae of the insect C. cephalonica was investigated. That Se is well tolerated by C. cephalonica upto an added level of 2 ppm in the diet is suggested by the observed increase in body weight, total protein, and succinate dehydrogenase levels. Significant increases in the State 3 respiration ensued with Se supplementation up to 2 ppm in the mitochondrial oxidation of D-glycerol 1-phosphate, succinate and NADH, along with concomitant unaltered State 4 respiration, leading to enhanced RCR values. Maximal uptake of75Se was registered in the larvae maintained on basal diet when subjected to short-term exposure to 0.5 ppm75Se level. When exposure level was further increased up to 20 ppm, the observed decrease in the uptake of75Se suggested that Se status of larvae itself controlled the tissue uptake. Subcellular distribution pattern revealed maximal incorporation of75Se (cpm/g tissue) in the supernatant fraction, whereas, maximal specific75Se activity (cpm/mg protein) was associated with the mitochondrial fraction. Autoradiography of the soluble fractions indicated the presence of single selenoprotein in the larval group with short term 2 ppm75Se exposure. Inherent Se controls both the extent and the nature of distribution of mitochondrial75Se incorporation. Uptake of45Ca by the insect mitochondria was enhanced by dietary Se up to 2 ppm but was unaffected by addition of in vitro75Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies. © 1994 Humana Press Inc.

Metabolic relevance of selenium in the insect Corcyra cephalonica - Uptake of75Se and subcellular distribution

The tissue uptake and distribution of injected [75Se]-sodium selenite as a variance with time and as influenced by dietary selenium status was followed in the tissues of Japanese quails, Coturnix coturnix japonica. Quails maintained on a low selenium semipurified (basal) diet and basal diets supplemented with 0.2 and 2.0 ppm selenium as sodium selenite were injected intraperitonially with75Se as sodium selenite (2.8 microcuries). The injected75Se was monitored in blood, liver, kidney, heart, and testis at 24, 72, and 144 h after injection. Maximal uptake of the injected75Se was observed in tissues of quails maintained on basal diet. The uptake of75Se in tissues in general was determined by the dietary Se status. Among the organs studied, kidney had the maximal level of75Se, 0.2 ppm (μg/g wet tissue) followed by liver, testis, and heart, but testis had the maximal level when the level per milligram of protein was considered, about 3.0 ng/mg protein, followed by liver, kidney, and heart. About 10-20% of the tissue75Se was located in the mitochondria and 50-60% in the post-mitochondrial supernatant fractions in all dietary Se levels. Significant incorporation of75Se in the mitochondrial membrane was observed. The percent distribution ratio between the membrane and matrix fractions of the mitochondria remained constant at all dietary Se levels which, in liver was 65:35, in kidney 55:45, and in testis 75:25. However, in heart mitochondria, the distribution of75Se between membrane and matrix varied with dietary Se status, the ratio being 82:18 in the basal group, and 72:28 and 41:59 in the 0.2 and 2.0 ppm Se-supplemented groups, respectively. This is indicative of a preferential uptake of75Se in the mitochondrial membrane in conditions of deficiency. About 40-60% of the mitochondrial membrane-associated75Se was released upon Triton treatment in all the organs. Of the membrane-bound75Se, about 10-15% was acid-labile in liver and kidney and 25% in the heart tissue. Possibilities of tissue specific roles, especially in the heart mitochondrial membrane-related processes, are indicated for selenium. © 1987 The Humana Press Inc.

Selenium-mediated biochemical changes in Japanese quails - Tissue uptake and distribution of injected75selenium labeled sodium selenite in relation to dietary selenium status

Biomethanation of organic matter is now recognized as a viable alternative for production of energy. Among various biomass sources screened, Leucaena leucocephala, having a high biomethanation rate, has been identified as a potential substrate for large-scale methane generation. During semi-continuous fermentations at 30 °C with volatile solids (VS) ranging from 1.0-2.5 g l-1 at hydraulic retention time (HRT) ranging from 10-18 days, the yield of product gas per gram of volatile solids input was about 0.45-0.601 in the case of L leucocephala and 0.15-0.201 from cow-manure. Mass spectrometric analysis of the product gas from L leucocephala indicated a methane content of 78-80%. Batch fermentation for 80 days with input volatile solids of 40-44 g in a 21 digester resulted in a gas yield of 0.87 l g-1 volatile solids input for L leucocephala and 0.33 l g for cow-manure. The complex degradation of solid organic matter involves multiphase interactions between microbes and their environment; optimisation and separation of predominantly acidogenic and methanogenic species was achieved in a multi-stage digester with separate compartments. This design was used for degradation studies of L. leucocephala, which, from the results presented, appears to be a good candidate for an 'energy-farm' for large-scale biomethanation. © 1986.

Fuel

Biomethanation of Leucaena leucocephala: a potential biomass substrate

Advances in Enzymology - and Related Areas of Molecular Biology Advances in Enzymology and Related Areas of Molecular Biology

The Respiratory Chain and Oxidative Phosphorylation

Journal	Biological Trace Element Research
Publisher	Humana Press
ISSN	01634984
Open Access	No