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-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.     

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.