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Biomedical subjects

S C Robinson

Publications and source records attributed to S C Robinson.

At least 19 recordsLinked to original sources
PubMed2002

A comparison of the process issues in expressing the same recombinant enzyme periplasmically in Escherichia coli and extracellularly in Streptomyces lividans.

The choice of a host for the production of a biological molecule will have a significant effect on isolation and purification procedures employed. This paper makes a comparison between the production of a single enzyme, a recombinant alpha-amylase, in Escherichia coli and Streptomyces lividans, on a small scale. It defines the differences in the cultivation and in the isolation stages and also describes the impact of the expression system on later downstream processing steps. At the cultivation stage, the specific productivity of the E. coli in units per gram per hour is four times that of the S. lividans while the total biomass yields are of the same order. The initial volume for downstream processing of S. lividans is six-fold larger and the total protein released into the extracellular medium is three times greater than E. coli, however, the recoverable yield from the E. coli is a fifth of that obtained from the S. lividans and requires three additional stages prior to chromatography. Even with these stages the final specific activity is 64% of the S. lividans. The results indicate the need to consider the whole process when making such comparisons.

Biomass↗
PubMed1994

Macrosomia: maternal and fetal outcome.

This retrospective case--control study analyses the prevalence and outcome of macrosomia in a part of the underdeveloped world. Out of 6,093 deliveries at a large tertiary care centre, 234 (3.8%) were macrosomic. Maternal risk factors associated with the condition included age over 35, obesity, grand multiparity, postmaturity and impaired glucose tolerance. Operative deliveries were more common as was shoulder dystocia, birth trauma, fetal distress, the need for neonatal intensive care and perinatal loss.

Case-Control Studies↗
PubMed1993

Characteristics of menopause in three socioeconomic urban groups in Karachi, Pakistan.

To determine age, symptoms and treatment choices in Pakistani women with spontaneous menopause, three groups in Karachi were interviewed using a structured questionnaire. The groups consisted of 250 poor slum dwellers, 250 middle class clinic attenders and 150 wives of retired military officers. Interviews were carried out in 1989 and 1990 by members of a team from the Aga Khan University consisting of a gynaecologist, a community health physician and two senior medical students. All interviewees had natural menopause at least 12 months previously. The results showed a mean age of 47 years for menopause in all groups. One in five women were symptomatic in the poorest group but one in two were in the other groups. Treatment was sought by 6% in the poor group, 26% of the middle class group and 38% of the most privileged group. Age at menopause was 4 years earlier than in most reports and fewer women had menopausal symptoms. These urban women may not represent the situation across the country but, as life expectancy in Pakistan is rising (now 56.4 years for women), menopausal problems may increase.

Adult↗
PubMed1992

Cardiac function in rats with acute renal failure.

Inotropic responses of isolated cardiac preparations from rats with glycerol-induced acute renal failure (ARF) were recorded, following a range of cardiac stimulants. Left atria of rats with ARF showed diminished inotropic responses only to the calcium agonist Bay K 8644 (methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyl-phenyl)-pyridine-5 -carboxylate) whilst right ventricular strips exhibited reduced responses to isoprenaline, 3-isobutyl-1-methylxanthine, Ca2+ and Bay K 8644. Investigations of cardiac mitochondrial respiration indicated that there is a site-unspecific 'pseudo' uncoupling of oxidative phosphorylation in ARF but that electron transport is unaffected. This uncoupling of oxidative phosphorylation did not have any detectable effect on either levels of total adenine nucleotides and creatine phosphate or cellular energy charge. Measurements were also made of the activity of pyruvate dehydrogenase which provides an index of mitochondrial Ca2+ levels. The proportion of pyruvate dehydrogenase in its active form was threefold higher following isoprenaline injection in hearts of rats with ARF compared with controls. The results suggest that in hearts of rats with ARF there is a change in the number, affinity, efficacy or coupling of the dihydropyridine receptor on the L-type calcium channel. Moreover, in the ventricle, a defect in cellular Ca2+ control, resulting in an increase in mitochondrial Ca2+ uptake, may contribute to the depression of inotropic response to the range of cardiac stimulants tested.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Leiomyoma in the hand. A case report.

A 60-year-old woman developed an avascular leiomyoma arising from a digital artery in the thumb and was successfully treated by en bloc excision. Leiomyomas in the hand are very rare, and thus the diagnosis will seldom be made on clinical evaluation. They may be more painful than other common, benign tumors, however, and may originate from a digital artery. Preoperative evaluation of vascular function may give a clue to the presence of a leiomyoma. A spectrum of vascular smooth-muscle tumors from very vascular to relatively avascular is noteworthy.

Arteries↗
PubMed1989

Validation of the use of the lipophilic thiocyanate anion for the determination of membrane potential in Ehrlich ascites tumor cells.

The utility of the lipophilic anion thiocyanate (SCN-) as a probe for the indirect estimation of the cell membrane potential (Vm) in Ehrlich ascites tumor cells has been evaluated by comparison to direct electrophysiological measurements. SCN accumulation is consistent with first-order uptake into a single, kinetically-identifiable cellular compartment, achieving steady-state distribution in 20-30 min at 22 degrees C. The steady state distribution ratio ([SCN-]e/[SCN-]e) in physiological saline is 0.44 +/- 0.02. Treatment of the cells with propranolol (0.13 mM), an activator of Ca2+ dependent K+ channels, reduces the steady-state distribution ratio to 0.19 +/- 0.02. Conversely, treatment with BaCl2 (10 mM), an antagonist of the pathway, increases the SCN- distribution ratio to 0.62 +/- 0.01. The equilibrium potentials (VSCN) calculated under these conditions are virtually identical to direct electrophysiological measurements of the Vm made under the same conditions. The effect of varying extracellular [K+] ([K+]e) in the presence of constant [Na+]e = 100 mM has also been tested. In control cells, elevation of [K+]e from 6 to 60 mM reduces VSCN from -20.6 +/- 1.0 to -13.2 +/- 1.2 mV. Again, microelectrode measurements give excellent quantitative agreement. Propranolol increases the sensitivity of the cells to varying [K+]e, so that a 10-fold elevation reduces VSCN by approximately 31 mV. BaCl2 greatly reduces this response: a 10-fold elevation in [K+]e yielding only a 4-mV reduction in VSCN. It is concluded that the membrane potential of Ehrlich cells can be estimated accurately from SCN- distribution measurements.

Animals↗
PubMed1988

Direct experimental evidence for competitive inhibition of dihydrofolate reductase by methotrexate.

Steady-state enzyme kinetic techniques at very low enzyme concentration (0.4 nM) were used successfully to measure the inhibition constant (53 pM) for the dissociation of methotrexate from the ternary complex of methotrexate, NADPH and dihydrofolate reductase from Lactobacillus casei; and to demonstrate unequivocally that the inhibition was, indeed, competitive with respect to dihydrofolate.

Binding, Competitive↗
PubMed1985

An anomalous flexor digitorum superficialis muscle-tendon unit associated with ulnar neuropathy. A case report.

A previously undescribed accessory flexor digitorum superficialis muscle-tendon unit was discovered on surgical exploration of the wrist in an 18-year-old girl with symptoms of distal ulnar neuropathy and a volar soft-tissue mass. Excision of the muscle-tendon unit resulted in complete resolution of symptoms. The preoperative diagnosis of an accessory muscle is difficult, being commonly mistaken for synovitis, ganglia, or tumor.

Adolescent↗
PubMed1983

The use of HgCl2 to evaluate the cosubstrate: amino acid transport stoichiometry in Ehrlich ascites tumor cells.

Recent investigations have indicated that cellular rheogenic properties may interfere with the correct estimation of Na+ and amino transport stoichiometry. We have reevaluated the stoichiometry of Na+ and alpha-aminoisobutyric acid (alpha-AIB) cotransport in Ehrlich ascites tumor cells depleted of Na+ and ATP by incubation in Na+-free HEPES-buffered medium (pH 7.2) containing 160 mM K+ and 2.5 microM valinomycin. Transfer of the cells to a medium with 10 mM 22Na+, 10 mM 3H-AIB, and 150 mM K+ resulted in an enhancement of Na+ flux above basal levels, which represents 0.6 of the AIB uptake. Under these conditions the membrane potential, -7.0 +/- 0.1 mV (SEM), does not change with the addition of AIB, -7.3 +/- 0.6 mV (SEM). HgCl2 (10 microM) added to the medium inhibited AIB flux and AIB-stimulated Na+ flux by 45-50% but did not change the coupling ratio. HgCl2 (10 microM) does not inhibit the basal Na+ flux nor does it affect cellular Na+ or K+ content. In physiological medium cotransport is electrogenic. The membrane potential of Ehrlich cells in physiological medium is -22.3 +/- 0.8 mV (SEM) and depolarizes to -16.7 +/- 0.7 mV (SEM) upon addition of AIB. Under these conditions the coupling ratio was highly variable but the ratio of codepression is 0.90 +/- 0.02 (SEM) in the presence of HgCl2 (10 microM). These results are consistent with a model (Smith and Robinson, 1981) in which the stoichiometry is one cosubstrate molecule per molecule of alpha-AIB. We suggest that H+ provides the alternative cosubstrate in this low Na+ environment and that in high Na+ medium the Na+:AIB stoichiometry approaches 1:1.

Amino Acids↗
PubMed1983

Cauda equina lipoma presenting as acute neuropathic arthropathy of the knee. A case report.

A 36-year-old man with a painless, rapidly progressive, destructive lesion of the right knee proved to have neuropathic arthropathy. Rather than being a tumor, the destructive process was neuropathic in origin. Myelography revealed an unsuspected intradural lesion, which proved to be a benign lipoma, at the third and fourth lumbar levels. Excision of the lipoma and arthrodesis of the knee were successful. True intrathecal lipomas are rare lesions that become symptomatic during a period of many years; when they are removed the prognosis is generally good. As in the present case, in neuropathic joint disease the underlying neuropathy and its etiology may be quite subtle, joint destruction may be very rapid, and diagnosis is difficult.

Adult↗
PubMed1981

The effect of the fluorescent probe, 3,3'-dipropylthiadicarbocyanine iodide, on the energy metabolism of Ehrlich ascites tumor cells.

The fluorescent dye, 3,3'-dipropylthiadicarbocyanine iodide, is frequently used to estimate the cell membrane potential of small cells. We have tested the effects of this dye on glycolytic rate, O2 consumption, and cellular ATP content in Ehrlich ascites tumor cells. Addition of the dye to steady state cells in the absence of glucose induces a rapid depletion (half-time approximately equal to 5 min) of cellular ATP, which is secondary to a 76% inhibition of O2 consumption. Aerobic glycolysis is stimulated by 76%. Valinomycin produces an additional stimulation of acid production. Our findings indicate that this fluorescent dye alters energy metabolism of Ehrlich ascites tumor cells. The response is consistent with primary inhibition of oxidative phosphorylation.

Adenosine Triphosphate↗
PubMed1981

Effect of H+ on the kinetics of Na+-dependent amino acid transport in Ehrlich ascites tumor cells: evidence for H+ as an alternative substrate.

The effects of H+ on the kinetics of alpha-aminoisobutyric acid (AIB) influx in Ehrlich ascites tumor cells have been investigated at different external Na+ concentrations. Elevation of [H+] in the presence of both high (154 mEq/l) and low (10 mEq/l) external Na+ leads to decreases in the maximum influx (Jmax) and increases in the apparent Michaelis-Menten constant (Km) for influx of AIB. In the virtual absence of external Na+ (0.96 +/- 0.04 mEq/l), alterations in [H+] are without measurable effect on AIB flux. Furthermore, addition of AIB (10 mM) to cell suspensions (pH 5.90) stimulates H+ uptake by the cells in either the presence or absence of Na+. The data are consistent with two kinetic models for Na+-dependent amino acid transport: an order bireactant (Na+-binding necessary before AIB binding) system or a random bireactant system. Both models require that H+ serve as an alternative substrate for Na+. The consistency of the models was tested by fit to data from the present study (not used to evaluate the kinetic parameters) and by prediction of the pH dependence of Na+-dependent amino acid transport compared to earlier studies.

Aminoisobutyric Acids↗