Baseline frequency of sister-chromatid exchanges (SCE) in newborn lymphocytes and its relationship to in vivo aging in humans

Heparinised cord blood from newborns and peripheral venous blood from three other age groups of individuals (1-75 years) have been cultured in vitro to obtain baseline frequencies of SCE and to see if the frequency of baseline SCE in vitro varies as a function of aging in vivo. The results demonstrate an age-dependent variation in the frequency of SCEs. Although the SCE frequency was lowest (5.10/cell) in 1-5-year-old infants, a significantly higher (P less than 0.001) frequency (8.97/cell) was observed in the cord blood of newborns. In old age, the level of SCE also increased. The plausible reason(s) for such observations is discussed.     

Metabolic relevance of selenium in the insectCorcyra cephalonica

Requirement, uptake, and subcellular distribution of Na₂ ⁷⁵SeO₃ in the larvae of the insectC. cephalonica was investigated. That Se is well tolerated byC. 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 ofin vitro ⁷⁵Se in the medium. A more fundamental role for Se in the mitochondrial energy metabolism emerges from these studies.     

Cell physiology and antibiotic production of Streptomyces coelicolor grown on solid medium

Summary In order to examine the physiology ofStreptomyces coelicolor when growing on solid media, we have employed a membrane overlay technique and used a new approach to extract substrate and product compounds from the agar. Comparisons made with liquid grown cultures indicate a change from non-growth associated productivity of actinorhodin in liquid culture, to growth associated production on agar plates. In contrast, the temporal control of methylenomycin production was virtually identical under both culture conditions. Considerable extracellular protein production was observed during growth on agar.     

Cell-bound cholinesterase inTrichoderma harzianum

Cell-bound cholinesterase enzyme activity is reported for the first time in the mycelium ofTrichoderma harzianum. This enzyme hydrolyzes both the acetylcholine and the butyryl thiocholine esters. TheK _m andV _max for choline ester are 0.69 mM and 1.0 nmol acid released min^–1 g^–1 protein. However, the thiocholine ester has aK _m value of 2.2 mM andV _max value of 3.33 nmol product formed min.^–1 g^–1 protein. The enzyme is inhibited by eserine, a true classical cholinesterase inhibitor.     

Protein sequences as random fractals

The analysis of primary sequences from a protein sequence data base suggests that the sequences can be considered as examples of constrained random fractals. Fractal dimensions of the positional distributions of the 20 residues along the chain have been calculated. These fractal dimensions can be used as indices of intrinsic preferences of various residues.     

Evaluation of scanning resolution,detector choice and detector orientation to be used for accurate and time-efficient commissioning of a 6MV clinical linear accelerator

The present study is aimed at exploring different scanning parameters, detectors and their orientations for time-efficient and accurate commissioning of a 6 MV clinical linear accelerator (LINAC). Beam profiles and percentage depth dose (PDD) curves were measured with a PTW dosimetry diode, a PTW Semiflex and a PinPoint ion chamber in different orientations. To acquire beam data, equidistant (step size of 0.5 mm, 1 mm, 2 mm and 3 mm) and fanline (step size of 2–0.5 mm, 2–1 mm, 3–0.5 mm and 3-1 mm) scanning modes were employed and data measurement time was recorded. Scan time per measurement point was also varied (0.2 s, 0.5 s and 1.0 s) to investigate its effect on the accuracy and acquisition time of beam data. Accuracy of the measured data was analyzed on the basis of the variation between measured data and data modeled by a treatment planning system. Beam profiles (particularly in penumbra region) were found to be sensitive to variation in scanning resolution and showed an improved accuracy with decrease in step size, while PDD curves were affected negligibly. The accuracy of beam data obtained with the PTW dosimetry diode and the PinPoint ion chamber was higher than those obtained with the PTW Semiflex ion chamber for small fields (2?×?2 cm² and 3?×?3 cm²). However, the response of the PTW diode and the PinPoint ion chamber was significantly indifferent in these fields. Furthermore, axial orientation of the PTW Semiflex ion chamber improved accuracy of profiles and PDDs as compared to radial orientation, while such a difference was not significant for the PinPoint ion chamber. It is concluded that a scan time of 0.2 s/point with a fanline scanning resolution of 2–1 mm for beam profiles and 3 mm for PDDs are most favorable in terms of accuracy and time efficiency. For small fields (2?×?2 cm² and 3?×?3 cm²), a PinPoint ion chamber in radial orientation or a dosimetry diode in axial orientation are recommended for both beam profiles and PDDs. If a PinPoint ion chamber and a PTW dosimetry diode are not available, a Semiflex ion chamber in axial orientation may be used for small fields.

     

Improved ethanol tolerance and production in strains of Clostridium thermocellum

Two Clostridium thermocellum strains were improved for ethanol tolerance, to 5% (v/v), by gradual adaptation and mutation. The best mutant gave an ethanol yield of 0.37 g/g substrate, with a growth yield 1.5 times more than its parent. Accumulation of acids and reducing sugars by the mutant strain with 5% (v/v) ethanol was lower than that of the parent strain with 1.5% (v/v) ethanol.     

Human and animal mesenchymal progenitor cells from bone marrow: Identification of serum for optimal selection and proliferation

Summary An undifferentiated subset of cells within the stromal cell population of bone marrow in postnatal mammals retains the capacity to differentiate along osteogenic, adipogenic, fibroblastic, and chondrogenic lines. These cells, which are referred to as mesenchymal stem cells (MSCs), can be maintainedin vitro and expanded in number through a process of subculturing. MSCs are maintained in culture in medium supplemented with 10% fetal bovine serum (FBS). It is believed that certain, as yet unidentified, serum components play critical roles in the attachment and proliferation of MSCs. Commercially available FBS is poorly characterized and may vary in composition and quality from lot to lot. This study describes a method for the selection of lots of FBS that best support maintenance of the undifferentiated state, mitotic expansion of MSCsin vitro, and retention of multilineage developmental potential in response to appropriate cues.