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Biomedical subjects

A L Taylor

Publications and source records attributed to A L Taylor.

At least 91 records · Page 5Linked to original sources
PubMed1971

Genetic analysis of diaminopimelic acid- and lysine-requiring mutants of Escherichia coli.

Several diaminopimelic acid (DAP)- and lysine-requiring mutants of Escherichia coli were isolated and studied by genetic, physiological, and biochemical means. The genes concerned with DAP-lysine synthesis map at several different sites on the E. coli chromosome and, therefore, do not constitute a single operon. Three separate loci affecting DAP synthesis are located in the 0 to 2.5 min region of the genetic map. The order of the loci in this region is thr-dapB-pyrA-ara-leu-pan-dapC-tonA-dapD. Two additional DAP genes map in the region between min 47 and 48, with the gene order being gua-dapA-dapE-ctr. The lys locus at min 55 determines the synthesis of the enzyme DAP decarboxylase, which catalyzes the conversion of DAP into lysine. The order of the genes in this region is serA-lysA-thyA.

Carboxy-Lyases↗
PubMed1971

Mutants of Escherichia coli with a growth requirement for either lysine or pyridoxine.

Two distinct phenotypic classes of lysine requiring auxotrophs of Escherichia coli are described. Mutants of the LysA class produce little or no active diaminopimelic acid (DAP) decarboxylase and specifically require lysine for growth. Mutants of the LysB class produce a cryptic DAP decarboxylase which can be activated both in vivo and in vitro by higher than normal levels of its cofactor, pyridoxal 5'-phosphate. The LysB mutants have an alternate requirement for lysine or pyridoxine. Both LysA and LysB mutations map at 55 min, close to the thyA locus of E. coli. The association between pyridoxal phosphate and DAP decarboxylase appears to be much weaker in LysB mutants than in wild-type bacteria, and the mutant enzyme also sediments more slowly than wild-type enzyme in sucrose density gradients. The results suggest that the LysB mutations alter a specific region (or subunit) of the enzyme molecule which is needed to stabilize the binding of pyridoxal phosphate. These studies help to resolve certain contradictory observations on DAP decarboxylase reported earlier and may have relevance to pyridoxal phosphate enzymes in general. Prototrophic revertants of LysB mutants arise by second site mutations that result in increased availability of intracellular pyridoxal phosphate. These revertants appear to be derepressed for pyridoxine biosynthesis.

Amino Acids↗
PubMed1971

Electron microscopic evidence for linear insertion of bacteriophage MU-1 in lysogenic bacteria.

Temperate bacteriophage Mu-1 was used to generate a lysogenic derivative of the F'lac episome of Escherichia coli. Intact, covalently circular molecules of F'lac and lysogenic F'lac Mu(+) deoxyribonucleic acid (DNA) were isolated and examined by electron microscopy. The mean contour lengths of F'lac and F'lac Mu(+) molecules were 37.6 +/- 0.4 mum and 53.2 +/- 0.4 mum, respectively. The mean difference, 15.6 mum, is similar to the mean contour length of 12.9 +/- 0.1 mum obtained for linear DNA molecules released by osmotic shock from mature phage Mu-1 virions. These results provide direct physical evidence that phage Mu-1 integrates by linear insertion of its genome into the DNA of lysogenic host bacteria. Chemical and physical analyses of phage Mu-1 DNA indicate that it is similar to E. coli DNA in respect of gross base composition, buoyant density, and melting temperature.

Adenine↗
PubMed1969

Metabolic clearance and production rates of human growth hormone.

The metabolic clearance rate (MCR) of human growth hormone (HGH) was determined by the constant infusion to equilibrium technique utilizing HGH-(125)I. 22 control subjects had a MCR of 229 +/-52 ml/min (mean +/-SD). No difference was evident between sexes, or between various age groups. Patients with acromegaly demonstrated normal MCR's. Moreover, acute elevations of plasma growth hormone concentrations in normal subjects did not alter the MCR of HGH. The MCR was relatively constant from day to day and within the day when subjects were evaluated in the supine position. In contrast, the assumption of the upright position was associated with a mean 24% decrease in the MCR. These results were contrasted with the MCR of HGH observed in a small number of patients with altered thyroid function or diabetes mellitus. In six patients with hypothyroidism the MCR (131 +/-36 ml/min) was significantly decreased (P < 0.001); whereas the MCR in eight patients with hyperthyroidism (240 +/-57 ml/min) did not differ from control subjects. The MCR in eight patients with insulin-independent diabetes mellitus (IID) (185 +/-41 ml/min) and in eight patients with insulin-dependent diabetes mellitus (IDD) (136 +/-31 ml/min) were significantly different from control subjects (P = < 0.05 and P = < 0.001, respectively). These data were interpreted to indicate that the plasma HGH-removing mechanism(s) is not saturated at physiologic plasma HGH levels, that plasma HGH levels alone may not permit distinction between variations in pituitary release of the hormone and its rate of clearance from the plasma, and that the estimation of the MCR of HGH may help clarify the mechanism of abnormal plasma HGH responses to various stimuli. Production rates of HGH (PR) in control subjects (347 +/-173 mmug/min) were contrasted with hyperthyroid patients (529 +/-242 mmug/min, P < 0.05), hypothyroid patients (160 +/-69 mmug/min, P < 0.02), IID (245 +/-100 mmug/min, NS), and IDD (363 +/-153 mmug/min, NS). Considerable variability in the determination of the concentrations of immunoprecipitable HGH-(125)I and endogenous plasma HGH concentrations was encountered at apparent equilibrium conditions. Since both factors are necessary for the PR calculations, the wide 95% confidence limits of the PR's did not permit a clear interpretation of the significance of these observations.

Acromegaly↗
PubMedDate not supplied

Exercise capacity in pediatric heart transplant candidates: is there any role for the 14 ml/kg/min guideline?

A peak oxygen consumption (VO2) of < 14 ml/kg/min has been identified as a predictor of l-year mortality in adults with congestive heart failure (CHF) and is used as a criterion for listing for cardiac transplantation (OHT). The role of VO2 measurement in children awaiting OHT has not been thoroughly evaluated. We sought to assess the degree of exercise impairment and the clinical applicability of the 14 ml/kg/min rule in children awaiting OHT. Cardiopulmonary exercise test (CPT) and cardiac catheterization data in all patients listed for OHT during the period of 1995-2003 were reviewed. Fourteen patients with a mean age of 15.5 +/- 2.9 years underwent CPT with no serious adverse events at an interval of 6.6 +/- 5.1 months prior to OHT. The etiology of CHF was multifactorial. Patients had impaired aerobic capacity with a mean peak VO2 of 20.4 +/- 6.8 ml/kg/min. Eleven of 14 patients (79%) had a peak VO2 higher than the adult cutoff value of 14 ml/kg/min. Pediatric ambulatory patients with CHF can safely undergo CPT. Because of age-related differences in oxygen consumption and varied etiologies of CHF a peak VO2 of < 14 ml/kg/min is not a useful criterion for listing for OHT in this population.

Adolescent↗