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S Smith

Publications and source records attributed to S Smith.

At least 901 records · Page 50Linked to original sources
PubMed1983

A number of different nuclear genes for the small subunit of RuBPCase are transcribed in petunia.

The sequences in the petunia genome which encode the small subunit polypeptides of the chloroplast enzyme ribulose-1,5-bisphosphate carboxylase have been characterized. Sequence analysis of four cDNA clones indicate that there are several distinct genes transcribed in leaf tissue. There is 8-9% nucleotide divergence between the transcripts however these changes do not alter the encoded amino acid sequence. Examination of nuclear DNA by Southern hybridization and analysis of cloned small subunit genes confirm that there are a number of different genes which encode this single protein.

Amino Acid Sequence↗
PubMed1983

Biosynthesis of medium-chain fatty acids by mammary epithelial cells from virgin rats.

Epithelial cells were isolated from the undifferentiated mammary glands of mature virgin female rats, and their lipogenic characteristics were studied. These cells synthesized predominantly medium-chain fatty acids, albeit at a low rate. In contrast, whole tissue from mammary glands of virgin rats synthesized predominantly long-chain fatty acids at a relatively higher rate, indicating that the lipogenic activity is dominated by the adipocyte component of the gland. Enzyme assays revealed that thioesterase II, the enzyme which regulates production of medium-chain fatty acids by the fatty acid synthetase, was present at a high activity in the undifferentiated mammary epithelial cells of virgin rats. Immunohistochemical studies confirmed this observation and showed that the regulatory enzyme was present exclusively in the epithelial cells lining the alveolar and ductal elements of the undifferentiated gland. This study demonstrates that the potential to elaborate tissue-specific medium-chain fatty acids is already expressed in the undifferentiated tissue of virgin rats and is not acquired as a result of the differentiation associated with the lactogenic phase of development. In this species mammary epithelial cells apparently synthesize predominantly medium-chain fatty acids at all stages of development, and only the overall rate of synthesis is increased on induction of the fatty acid synthetase during lactogenesis.

Animals↗
PubMed1983

The effect of aromatic CoA esters on fatty acid synthetase: biosynthesis of omega-phenyl fatty acids.

Aromatic carboxylic acids ingested by, or formed in, the body can be converted to the CoA derivatives but the possible metabolic fate of these thioesters has not been investigated extensively. We have examined the effects of two such thioesters, benzoyl-CoA and phenylacetyl-CoA, on the mammalian fatty acid synthetase. Benzoyl-CoA inhibited the enzyme, apparently by competing with acetyl-CoA and malonyl-CoA for substrate binding sites. Phenylacetyl-CoA, on the other hand, could replace acetyl-CoA as a primer for the fatty acid synthetase reaction; the product was almost exclusively omega-phenyldodecanoic acid. The Km of the synthetase for phenylacetyl-CoA was considerably higher than that for acetyl-CoA and the rate of synthesis of omega-phenyldodecanoic acid was only 16% of that of palmitic acid. Experiments in which the rate of synthesis and release of omega-phenyl moieties from the synthetase was compared with that of n-aliphatic moieties indicated that the rate limiting step was the initiation of chain growth from phenylacetyl-CoA; release of the synthesized acyl moieties by chain terminating thioesterases was equally rapid in the case of omega-phenyl and n-aliphatic acids. Possible metabolic consequences of the effects of these aromatic CoA esters on lipogenesis are discussed.

Acetyl Coenzyme A↗
PubMed1983

Benzodiazepine--specific and nonspecific tolerance following chronic flurazepam treatment.

Rats were given a flurazepam solution as their only water source for 4 weeks. The drug concentration was adjusted so the rats would consume 100-150 mg/kg daily. This treatment is known to cause a reduction in the number of specific benzodiazepine binding sites (receptor down-regulation) and tolerance to the locomotor impairment caused by the injection of a large test dose of flurazepam. Both the tolerance and the receptor down-regulation disappear within 24 hours after the end of chronic treatment. After 4 weeks of flurazepam treatment, rats were tested for locomotor impairment and loss of the righting response caused by pentobarbital, ethanol or diazepam. There was a small tolerance to pentobarbital. This lasted at least 4 days, but had disappeared by 7 days. Rats also had a small tolerance to ethanol, which disappeared between 24 and 48 hours after the end of chronic flurazepam treatment. In contrast, there was a large tolerance to diazepam, but this was gone by 24 hours after the end of chronic treatment. It appears that two types of tolerance develop during benzodiazepine treatment: (1) tolerance specific for benzodiazepines possibly mediated by receptor down-regulation, and (2) nonspecific tolerance, possibly analogous to that which develops during chronic barbiturate treatment.

Animals↗
PubMed1983

The use of thioesterase II as a rat mammary epithelial cell-specific marker.

The avidin-biotin-peroxidase complex immunoperoxidase technique was employed to determine the intercellular distribution of thioesterase II in rat mammary glands. This enzyme is responsible for shifting the product specificity of the fatty-acid synthetase enzyme complex from long to medium chain fatty acids. Thioesterase II was found exclusively in the cells lining the lumen of the ductal and alveolar structures in glands from mature virgin (150 days old) and pregnant rats. The ductal cell staining intensity was considerably less than that of the alveolar cells in the mature virgin rat glands. No immunoreactive thioesterase II was found in the stromal, adipose, vascular, or myoepithelial components of the gland in the developmental stages examined. In the glands from immature virgin rats (40-45 days old) thioesterase II was again found only in the epithelial cells lining the lumen of the ductal and end-bud structures although this layer was usually more than one cell thick. Quantitative determination of thioesterase II activity in cytosol preparations revealed similar levels in mammary fragments from enzymatically-dissociated glands obtained from mature virgins and in end buds derived from immature virgins, but somewhat higher levels in mammary structures derived from late-pregnant animals. These immunohistological and biochemical results demonstrate thioesterase II's usefulness as a mammary epithelial cell-specific marker.

Animals↗
PubMed1983

Response of end bud cells from immature rat mammary gland to hormones when cultured in collagen gel.

End buds from 4- to 5-week-old rat mammary glands were isolated and cultured within a rat tail tendon collagen gel matrix. Media containing equine serum or porcine serum and cholera toxin promoted growth, but not the production of casein or thioesterase II, nor did they induce a state of differentiation as assessed by cell ultrastructure. Medium supplemented with only 5% porcine serum, insulin and cholera toxin did not support growth or differentiation. However, when prolactin, estradiol, progesterone and hydrocortisone were added to this medium, growth was stimulated greatly and a differentiated state was induced as assessed by the production of casein and thioesterase and by the appearance of a highly secretory ultrastructure.

Animals↗
PubMed1983

Fanconi's anemia: a cytogenetic study on lymphocyte and bone marrow cultures utilizing 1,2:3,4-diepoxybutane.

Fanconi's anemia (FA) is an autosomal recessive genetic trait characterized by congenital abnormalities, pancytopenia with a late onset, and increased chromosome instability. A great deal of heterogeneity exists in the disease, making an early correct diagnosis very difficult. Previously chromosome instability was used as a diagnostic tool but was found to be unreliable. Auerbach et al. have described the use of a difunctional alkylating agent, 1,2:3,4-diepoxybutane (DEB), in lymphocyte, fibroblast, and amniotic fluid cultures for the accurate diagnosis of homozygotes and heterozygotes for the FA gene. We report here the findings on lymphocyte and bone marrow cultures from 18 FA homozygotes and 17 family members. Statistical analysis of the results with DEB at different concentrations showed a significant increase in induced chromosome breakage rates for homozygotes and heterozygotes when compared to those for a control group. The bone marrow cultures gave similar results.

Anemia, Aplastic↗
PubMed1983

Correlation of spontaneous microaggregate formation with the severity of trauma in man.

Blood samples were obtained from 237 consecutive injured patients before any resuscitation. Microaggregate (MA) formation was measured by the screen filtration pressure (SFP) technique. Arterial blood gases were analyzed concomitantly and the respiratory index (RI) calculated. An Injury Severity Score (ISS) was calculated for each patient. The results show a significantly larger amount of trauma in the patients with the higher SFP results (p less than 0.001). Associated with the increase in the amount of MA formation was a significant decrease in arterial pO2 (p less than 0.05) and a significant rise in the RI (p less than 0.005), suggesting a correlation between MA formation and pulmonary impairment. Attempts to prevent or resolve MA formation may result in a decrease in the incidence or severity of post-traumatic pulmonary insufficiency.

Adolescent↗
PubMed1983

Changes in motoneurone firing rates during sustained maximal voluntary contractions.

Tungsten micro-electrodes have been used to record the electrical activity of single motor units in the human adductor pollicis during maximal voluntary contractions. The potentials were characteristic of those from single muscle fibres. In brief maximal contractions, the firing rates of over 200 motor units were obtained from five normal subjects. Four subjects had a similar range (mean 26.4 +/- 6.5 Hz) while the fifth was slightly higher (35 +/- 7.4 Hz). When maximal voluntary force was sustained for 40-120 s, there was a progressive decline in the range and mean rate of motor-unit discharge. In the first 60 s, mean rates fell from about 27 Hz to 15 Hz. There was some evidence to suggest that those units with the highest initial frequencies changed rate most rapidly. It is suggested that this decline in motor unit discharge rates is not responsible for force loss, but that it may enable effective modulation of voluntary strength by rate coding to continue during fatigue.

Action Potentials↗
PubMed1983

Methylenetetrahydrofolate dehydrogenase - methenyltetrahydrofolate cyclohydrolase - formyltetrahydrofolate synthetase from porcine liver: evidence to support a common dehydrogenase-cyclohydrolase site.

The cyclohydrolase activity of the trifunctional enzyme methylenetetrahydrofolate dehydrogenase - methenyltetrahydrofolate cyclohydrolase - formyltetrahydrofolate synthetase is inhibited by NADP+, a substrate of the dehydogenase. This uncompetitive inhibition, shown also by 3-aminopyridine adenine dinucleotide phosphate (AADP), indicates formation of dead-end complexes consisting of enzyme-nucleotide-methenyltetrahydrofolate. Chemical modification with diethylpyrocarbonate inactivates the dehydrogenase and cyclohydrolase but not the synthetase. Folate, but neither NADP+ nor AADP, protects both activities against modification. However, NADP+ potentiates the protection by folate by decreasing the apparent Kd for that ligand approximately sixfold. Chemical modification with phenylglyoxal also inactivates both the dehydrogenase and cyclohydrolase activities. Neither activity was protected by NADP+ or folate alone; however, the combination of NADP+ and folate protected both activities. These results are consistent with a model in which the dehydrogenase and cyclohydrolase activities share a common folate binding site.

Aminohydrolases↗
PubMed1983

Neuroendocrine mechanisms controlling the onset of female puberty: the rat as a model.

The advent of female puberty represents the culmination of a diversity of developmental processes which affect all components of the reproductive axis. Development of neuroendocrine reproductive functions proceeds in a harmonious and interrelated manner. No unique 'trigger' of puberty can be discerned, but rather puberty represents the climax of a cascade of events, finely interconnected throughout the continuum of sexual maturation. A resetting of the hypothalamic 'gonadostat' to steroid negative feedback appears to be a phenomenon associated with puberty, but not its cause. Although the central nervous system plays a pivotal role in the development of the ovary, it is the acquisition of ovarian ovulatory capacity which finally determines the timing of the first preovulatory surge of gonadotropins. In contrast to primates, development of the central component of estradiol positive feedback is an early event in the female rat. However, in most species--including the rat--amplification (or initiation) of a particular, synchronous pattern of LHRH release appears essential for the initiation of puberty. The mechanisms underlying this functional change of the LHRH secreting system are not clearly understood. In the rat, ovarian development proceeds under the influence of gonadotropins, and the somatomammotropins PRL and GH. More intriguingly, evidence is now emerging that the central nervous system may convey direct information to the ovary via the ovarian nerves, thus providing a hormone-independent fine tuning for its control. Upon reaching adequate development, the ovary through its secretory products, acts on an already competent hypothalamic-pituitary axis to activate the central component of estradiol positive feedback.

Animals↗
PubMed1983

Induction of a T-cell mediated suppressor activity by soluble products from antigen-specific helper/inducer human T-cell lines.

Influenza virus-specific (A/X31) long-term cultured human T-cell lines belonging to the helper/inducer T-cell set, produce high potency antigen specific helper factors which induce in vitro antibody production to A/X31 by autologous B cells, as well as small and variable amounts of non-specific helper factors. When added to unseparated peripheral blood mononuclear cells, both cultured T cells and their supernatants suppress in vitro antibody synthesis as measured by a solid phase enzyme-linked immunoassay, and T-cell proliferation to antigens and allogeneic cells, but not to mitogens. This phenomenon was further analysed and could be separated into several steps: (i) the production of suppressor inducer factor(s) by the T-cell lines which are distinct from the helper molecules; (ii) activation of T cells belonging to the suppressor/cytotoxic subset as defined by monoclonal antibodies, a process which is antigen-independent and non-genetically restricted, and is optimal with 18 hr incubation; (iii) the activated T cells non-specific suppress antibody production and antigen-induced or allogeneic cell-induced T-cell proliferation. Thus, antigen-specifically activated T-inducer cells exert multiple activities, including specific and non-specific help and non-specific induction of T suppressor cells.

Antibodies, Viral↗
PubMed1983

Monoclonal antibody characterization of surface antigens in childhood T-cell lymphoid malignancies.

Although childhood T-cell acute lymphocytic leukemia (T-ALL) and T-cell non-Hodgkin's lymphoma (T-NHL) have certain clinical features in common, T-ALL carries a notably poorer prognosis than does T-NHL. To determine whether the malignant cells from patients with these disorders are distinguishable, we examined bone marrow and/or blood from 51 children with T-ALL and tumor biopsy specimens from 17 with T-NHL, using a panel of monoclonal antibodies directed against T-cell differentiation antigens. We found considerable phenotypic heterogeneity in both T-ALL and T-NHL. Of the T-ALL (defined by greater than 25% blasts in the bone marrow) patients, 33% demonstrated a surface antigen pattern consistent with the earliest thymocyte stage of T-cell development (T9+ and/or T10+, or T6-/T4-/T8-/T3-), 37% were of a midthymocyte stage (T6+, and/or simultaneous expression of T4-helper and T8-suppressor antigens), and 30% expressed surface antigen patterns found on mature thymocytes (T3+, variable expression of other antigens). In contrast, tumor cell phenotypes in the 17 T-NHL patients were approximately equally distributed between mid- and mature thymocyte phenotypes. No NHL samples were classified as the early thymocyte phenotype. Clinical features as related to specific T-ALL immunophenotypes are presented, and the implications of these findings in regard to the current understanding of the differences in tumor biology between T-ALL and T-NHL are discussed.

Antibodies, Monoclonal↗