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Biomedical subjects

A Singh

Publications and source records attributed to A Singh.

At least 541 records · Page 30Linked to original sources
PubMed1991

Fusarium oxysporum: status in bioethanol production.

Fermentation of lignocellulosic materials to ethanol and other solvents provides an alternative way of treating wastes and producing chemical feedstocks and fuel additives. Considerable efforts have been made in past 10 years to improve the process based on lignocellulosic biomass and hydrolysate that contains a complex mixture of sugars, decomposition products of sugars, and sometimes the inhibitory levels of soluble lignin. Despite the relative abundance of D-xylose in crop and forest residues it has not been found efficiently fermentable by most of the microorganisms. Recent research has revealed that D-xylose may be fermented to ethanol and organic acids. Recently, several strains of Fusarium oxysporum have been found to have potential for converting not only D-xylose, but also cellulose to ethanol in a one-step process. Distinguishing features of F. oxysporum for ethanol production in comparison to other organisms are identified. These include the advantage of in situ cellulase production and cellulose fermentation, pentose fermentation, and the tolerance of sugars and ethanol. The main disadvantage is the slow conversion rate when compared with yeast.

Biotechnology↗
PubMed1991

Circadian variations in circulating plasma sex steroids in female catfish, Clarias batrachus (Linn.).

Estradiol (E2) and 17 alpha-hydroxyprogesterone (17 alpha-OHP) levels exhibited significant circadian rhythms in the prespawning phase of the reproductive cycle. Pattern of rhythm was unimodal. Whereas, in the spawning phase E2 levels did not show significant fluctuations in their daily cycle whereas 17 alpha-OHP levels showed significant rhythm (P less than 0.001). Amplitude of rhythm of E2 was greater in prespawning phase while 17 alpha-OHP showed greater amplitude in spawning phase.

17-alpha-Hydroxyprogesterone↗
PubMed1991

Alteration of primate ovary surface epithelium by exposure to hexachlorobenzene: a quantitative study.

Hexachlorobenzene (HCB) is a fungicide and a pollutant of increasing concern in industrialized regions of the world. Reproductive failure is one of the effects of HCB upon mammals. Alteration of cell shape in the ovary surface epithelium (OSE) of Cynomolgus monkeys following oral administration of HCB was observed in this study. At the lowest dose used, 0.1 mg/kg body weight, a dosage that is associated with follicular degeneration, HCB caused quantifiable changes in length-to-width ratios of OSE. Measurement of cell shape by light microscopy offers a reliable indication of OSE changes induced by HCB.

Animals↗
PubMed1991

Exercise-induced changes in blood minerals, associated proteins and hormones in women athletes.

The acute effects of prolonged exercise on the body's distribution of trace minerals in women athletes has not been examined. To this end, plasma concentrations of zinc, copper, and iron; erythrocyte zinc (EZn) and copper (ECu); and the associated proteins, ceruloplasmin and transferrin were measured in 38 highly trained women runners under resting conditions and again after running a competitive 26.2 mile marathon. The hormones, cortisol (C), estradiol (E2), prolactin (Prl), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were also measured because of reported effects of hormones on trace mineral distribution. Menstrual status was assessed by questionnaire: 8 women were in the follicular phase, 13 in mid-cycle, 8 in the luteal phase and 9 were amenorrheic (AM). Significant post-race increases were noted for all plasma minerals, associated proteins, and the hormones C and Prl, whereas EZn decreased. No significant changes in ECu, E2, FSH or LH were noted. Menstrual status in terms of cycle phase or amenorrhea did not appear to modify the response. Exercise-induced changes in minerals may reflect release from other tissues and/or changes in the concentration of associated proteins. Whether these changes serve adaptive and/or specific functions during exercise is unknown.

Adult↗
PubMed1991

SEM surface structure of the adhesive organ of the hillstream fish Glyptothorax pectinopterus (Teleostei: Sisoridae) from the Garhwal Hills.

Glyptothorax pectinopterus has a well defined bilateral adhesive organ situated posteriorly to the mouth, between the opercular opening and the base of the pectoral fin. It narrows at its anterior and posterior end and is characterized by thin longitudinal ridges and grooves running almost parallel to the main body axis, but with a slight inclination posteriorly. The ridges all seem to converge towards the posteriorly localized middle pad. In conformity with the hillstream type of habitat, the ridges are surmounted by long, keratinized epidermal spines with hooked, curved or sucker-like tips. The hooked spines, in adhesion to the substratum, attach themselves firmly to organic material, while the sucker-tipped spines reinforce adhesion by generating vacua at innumerable scattered points. The effect of mechanical abrasion of the spines is minimized by a glandular secretion from the middle pad.

Animals↗
PubMed1991

Radiographic techniques for early detection of osteoporosis.

Sequelae of osteoporosis such as fracture and deformities usually occur when the bone mass has been severely reduced. Since the lost bone mass cannot be replaced, management of osteoporosis is aimed at preventing, halting, or retarding its progression. Early detection of osteoporosis and the identification of individuals at high risk for the disease are crucial if therapy is to be effective. Several radiographic techniques are currently available for osteoporosis screening, including dual photon absorptiometry (DPA), quantitative computed tomography (QCT), and dual-energy radiographic absorptiometry (DRA). This paper discusses the relative value and limitations of these techniques.

Absorptiometry, Photon↗
PubMed1991

Characterization of pseudomonal adherence to unwounded cornea.

This study examined binding of Pseudomonas aeruginosa to unwounded postnatal day (P) 5 immature mouse cornea. To determine whether the receptor molecule was protein or lipid in nature, the eyes were incubated in vitro with trypsin or lipase before bacteria were applied. Trypsin significantly increased bacterial binding, whereas lipase had no effect. To determine if enhanced binding after trypsin indicated exposure of a lipid or a protein receptor, the eyes were treated sequentially with trypsin, then lipase. Subsequent binding did not differ significantly from trypsin alone, indicating that the exposed receptor was not a lipid. Incubation of the P 5 eye with neuraminidase to remove sialylated residues also significantly enhanced binding at all times, and premixing of the inoculum with the enzyme before adherence testing increased binding at 15 and 30 min. The effects of a monosialoganglioside (GM1) and gangliotetraosylceramide (asialo GM1) were also examined. Incubation of eyes with GM1 or asialo GM1 produced no significant inhibition of bacterial binding, but premixing of the bacterial inoculum with GM1 or asialo GM1 before corneal application transiently decreased adherence. Fibronectin (FN) treatment of the P 5 eye, premixing FN with the bacterial inoculum before its ocular application, or similar treatment with N-acetylneuraminic acid (NANA) transiently inhibited binding. These data demonstrate that pseudomonal binding to the unwounded eye is not lipase sensitive and is enhanced by trypsin treatment which exposes a lipase insensitive receptor and by neuraminidase which removes sialylated residues. It is not inhibited by pretreatment of the eye with either GM1 or asialo GM1 and is transiently inhibited by pretreatment of the eye or the inoculum with NANA or FN.

Animals↗
PubMed1991

Surface epithelium of the ovary following oral administration of hexachlorobenzene to the monkey.

Hexachlorobenzene (HCB) is a toxic and carcinogenic chemical that has been implicated in female reproductive dysfunctions, including destruction of ovarian follicles in primates. The purpose of this study was to determine the effects of HCB on ovary surface epithelium (SE). Gelatin capsules containing HCB mixed with glucose were given to 16 cynomolgus monkeys housed under controlled conditions in dosages of 0.0, 0.1, 1.0, or 10.0 mg/kg body weight daily, for 90 days; the first group served as the control. At necropsy one ovary from each animal was removed, fixed in glutaraldehyde, and processed by conventional methods for examination by transmission electron microscopy. SE from the animals in control group consisted of a single layer of squamous-to-cuboidal cells which possessed microvilli and contained cytoplasm rich in organelles; the nuclei were placed in middle of the cells. Although the types of alteration were similar in the treated groups, the degree of severity increased with increasing dose levels. In the lowest dose group (0.1 mg/kg) tested, stratification of cells was observed in some areas. Many cells were tall columnar, highly irregular in outline, and showed signs of degeneration. The nuclei had migrated toward the apical surface. Cytoplasm contained a large number of lysosomes, and numerous vesicles, which may have been swollen endoplasmic reticulum. In the 10 mg/kg group the affected cells were in advanced stages of degeneration. These observations support the evidence that HCB is a potent reproductive toxicant. Further studies are required to establish the effects of this damage on reproductive performance.

Administration, Oral↗
PubMed1991

Single cell protein production by Aspergillus niger and its evaluation.

An efficient cellulolytic mold, Aspergillus niger AS-101 was used to produce single cell protein from alkalitreated corn cobs. Microbial biomass obtained after 6 days of fermentation was evaluated for its various quality components. Single cell protein product contained 30.4% crude protein and had an essential amino acid profile featuring a high lysine content and appreciable amounts of methionine and tryptophane. Product contained 12.9% fat which was comprised of all essential fatty acids. Product has 77% of in vitro dry matter digestibility, hence can be used to supplement the feed components of ruminents and other monogastric animals.

Amino Acids, Essential↗
PubMed1990

Superoxide dismutase as a regulatory switch in mammalian testicular steroidogenesis.

The delta 4-pathway of testosterone biosynthesis in leydig cells, widely believed to proceed through pregnenolone--greater than pregnenedione--greater than progesterone route catalyzed by 5 delta-3 beta-hydroxysteroid dehydrogenase and delta 5-delta 4-isomerase respectively is shown to pass through an alternate pathway mediated by superoxide dismutase and peroxidase. A built-in regulatory switch is incorporated in this route, with the superoxide dismutase inducible upon LH-stimulation of the leydig cells.

Animals↗
PubMed1990

Superoxide anion radical induces lipid phase transitions that mimic temperature-induced phase-transition phenomenon of membrane lipids.

A biological membrane is shown to undergo lipid-phase transition leading to increased membrane fluidity when exposed to extraneously generated superoxide anion radical. This phase-transition is several folds higher in magnitude when compared to the temperature-induced fluidity change at the transition temperatures. This finding could have significant importance since an altered membrane configuration may involve aspects of biochemistry, biophysics or physiology.

Animals↗
PubMed1990

Insertion of bacteriorhodopsin into polymerized diacetylenic phosphatidylcholine bilayers.

We have developed a method to incorporate the membrane protein bacteriorhodopsin into polymerized bilayers composed of a diacetylenic phosphatidylcholine, 1,2-bis(tricosa-10,12-diynoyl)-sn-glycero-3-phosphocholine (DC8,9PC) and a non-polymerizable phospholipid, dinonanoylphosphatidylcholine (DNPC). The extent of DC8,9PC polymerization in the bilayer was significantly improved when 2:1 mole ratio DNPC-DC8,9PC was used. Octyl glucopyranoside-solubilized bacteriorhodopsin was inserted into the polymerized DNPC-DC8,9PC bilayers by overnight incubation at 4 degrees C followed by dialysis to remove the detergent. The protein was inserted into the membranes after photo-polymerization to avoid inactivation of the protein due to the UV irradiation. The insertion of bacteriorhodopsin into the polymerized DNPC-DC8,9PC membranes was confirmed by density gradient centrifugation, UV/visible spectroscopy, and freeze fracture electron microscopy. The polymerized DNPC-DC8,9PC membranes containing bacteriorhodopsin were about 10% protein by weight. These results suggest that mixed lipid systems such as the DNPC-DC8,9PC can be used to improve both the extent of polymerization and the efficiency of membrane protein incorporation in the polymerized bilayer.

Bacteriorhodopsins↗
PubMed1990

General and kinetic properties of endoglucanase from Aspergillus niger.

Endoglucanase of Aspergillus niger AS-101 was partially purified by ammonium sulphate fractionation and molecular sieving on Sephadex G-200. The enzyme was found to be unstable on storage, however, it received some protection on the addition of BSA, glycerol or sodium azide. Glycerol also protected the enzyme from inactivation due to freezing and thawing. Studies on the effect of thiol group reagents revealed the involvement of -SH group(s) at the active site of enzyme. The enzyme was a metallo-protein or it required certain metal ions for activation. A variety of modulators such as macroionic compounds and metal ions showed varying effects on the purified endoglucanase.

Aspergillus niger↗
PubMed1990

Activation of iodine into a free-radical intermediate by superoxide: a physiologically significant step in the iodination of tyrosine.

A pivotal biochemical event in the thyroid physiology is identified unravelling a superoxide anion radical-mediated activation of iodine into an active I.- form, which could be the intermediate that is incorporated onto tyrosine. This active iodine species gives fairly stable spin-adducts with PBN that could be characterized using EPR spectroscopy. Thus, a long-lasting puzzle regarding the iodine intermediate formed before iodination of tyrosine seems to be solved.

Animals↗