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Biomedical subjects

M K Johnson

Publications and source records attributed to M K Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1989

The eyewitness suggestibility effect and memory for source.

We examined the possibility that eyewitness suggestibility reflects failures of the processes by which people normally discriminate between memories derived from different sources. To test this hypothesis, misled and control subjects were tested either with a yes/no recognition test or with a "source monitoring" test designed to orient subjects to attend to information about the sources of their memories. The results demonstrate that suggestibility effects obtained with a recognition test can be eliminated by orienting subjects toward thinking about the sources of their memories while taking the test. Our findings indicate that although misled subjects are capable of identifying the source of their memories of misleading suggestions, they nonetheless sometimes misidentify them as memories derived from the original event. The extent to which such errors reflect genuine memory confusions (produced, for example, by lax judgment criteria) or conscious misattributions (perhaps due to demand characteristics) remains to be specified.

Adolescent↗
PubMed1988

Sensitivity and selectivity of compounds interacting with neuropathy target esterase. Further structure-activity studies.

Assay of neuropathy target esterase (NTE) which accounts for about 70% of paraoxon-resistant phenyl valerate (PV) esterase activity of hen brain depends on the fact that it is selectively inhibited by mipafox. A previous study of structure/activity relationships (Biochem. Pharmac. 24, 797, 1975) has been extended. Among 14 potential substrates NTE hydrolysed phenyl phenoxyacetate and phenyl thiophenoxyacetate faster (1.5-1.7X) than PV, but selectivity of these substrates for NTE among the paraoxon-resistant esterases was only 35-52%. Seventy-seven other potential inhibitors (organophosphates, phosphonates, phosphoramidates, phosphinates and carbamates) were examined to determine I50NTE and effects on both NTE and "non-NTE" at 3-4 x I50NTE (I 85-95) and, where possible, at 6-20 X I50NTE. Hydrophophic inhibitors with small/flexible leaving groups were generally very inhibitory: several 2,2-dichlorovinyl phosphates and fluorides were active at low nanomolar concentrations. In the dichlorovinyl phosphate series increasing dialkyl chain length beyond n-pentyl decreased inhibitory power, presumably due to steric hindrance since the methyl/n-decyl ester was 15X more active than di-n-decyl. Chloro-substitution of both ortho-positions of a phenyl leaving group for benzylcarbamates reduced inhibitory power more than 20X but had little effect in a phenyl leaving group of methyl phenylphosphonates where the acyl-leaving group bond is longer and less subject to steric hindrance. N-phenylbenzohydroxamyl benzylcarbamate is 10X more potent than any previously described carbamate against NTE. Among stereo-isomers differences of activity ranged from less than 2- to 15-fold. Only diphenylphosphinyl fluoride appeared to be virtually specific for NTE: at 0.5-1 microM it inhibited ca.92% of NTE and 10-13% of "non-NTE" which is similar to the specificity found for 2,6-dichlorophenyl methyl phenylphosphonate which has been claimed to be specific. Diphenylphosphinyl fluoride has an advantage in that it is easily synthesized and should be protective rather than neuropathic, but it is not stable in store. We cannot repeat experiments purporting to show a substantial proportion of a second isozyme of NTE. However, according to first-order kinetics, concentrations of inhibitor greater than 6 X I50 should inhibit NTE greater than 98% and for 19 out of 26 compounds a residue greater than 3% (limit of precision) was found under these conditions: in nearly every case the quantity was 3-5%. This quantity may not be "true NTE" but it cannot be the target for organophosphate-induced delayed neuropathy since it is resistant to various neuropathic and protective compounds.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Subunit location of the iron-sulfur clusters in fumarate reductase from Escherichia coli.

The subunit location of the [2Fe-2S], [3Fe-4S], and [4Fe-4S] clusters in Escherichia coli fumarate reductase has been investigated by EPR studies of whole cells or whole cells extracts of a fumarate reductase deletion mutant with plasmid amplified expression of discrete fumarate reductase subunits or groups of subunits. The results indicate that both the [2Fe-2S] and [3Fe-4S] clusters are located entirely in the iron-sulfur protein subunit. Information concerning the specific cysteine residues that ligate these clusters has been obtained by investigating the EPR characteristics of cells of the deletion mutant amplified with a plasmid coding for the flavoprotein subunit and a truncated iron-sulfur protein subunit. While the results are not definitive with respect to the location of the [4Fe-4S] cluster, they are most readily interpreted in terms of this cluster being entirely in the flavoprotein subunit or bridging between the two catalytic domain subunits. These new results are discussed in light of the amino acid sequences of the two subunits and the sequences of structurally well characterized iron-sulfur proteins containing [2Fe-2S], [3Fe-4S], and [4Fe-4S] centers.

Amino Acid Sequence↗
PubMed1988

High doses of soman protect against organophosphorus-induced delayed polyneuropathy but tabun does not.

Organophosphorus-induced delayed polyneuropathy (OPIDP) is thought to result from organophosphorylation of neuropathy target esterase (NTE; formerly known as neurotoxic esterase), followed by an "aging" of the phosphorylated NTE. Protection against OPIDP should thus be achieved by production of an inhibited but "nonaging" NTE. Inhibited NTE produced in vitro by interaction with any of the four resolved isomers of soman aged negligibly (M. K. Johnson, D. J. Read, and H. P. Benschop, 1985a, Biochem. Pharmacol., 34, 1945-1951). Therefore both unresolved soman and the most inhibitory isomer (C(-)P(+)) were tested in adult hens for effects on NTE and for ability to produce OPIDP. With improved prophylaxis and therapy of acute intoxication, birds survived greater than 100 X LD50 of unresolved soman and did not develop OPIDP. One day after dosing, about half of brain and spinal cord NTE was in an unmodified (unaged) inhibited form; at this time eight survivors were challenged with a neuropathic dose of diisopropyl phosphorofluoridate (DFP). No neuropathy developed in four out of eight birds and mild to moderate signs were seen in the other four. Nine challenge control birds receiving DFP after solvent all developed severe neuropathy. Partial protection was seen in three out of three birds dosed prior to DFP challenge with sufficient C(-)P(+) isomer of soman (1.2 mg/kg sc) to convert about half of the spinal cord NTE to unaged inhibited form. Protection was not related to cholinergic shock. Two birds which survived out of eight pretreated with tabun (12 mg/kg sc) had about as much NTE inhibited as after soman administration but it was all in the modified (aged) inhibited form; these birds were not protected against DFP-induced neuropathy. A limited histopathologic examination showed that typical neurodegenerative lesions were seen only in birds with clear clinical neuropathy.

Animals↗
PubMed1988

Amnesia and second language learning.

The ability of an anterograde amnesic C.S. to learn a second language is assessed. First, her claim that she learned Italian while amnesic was examined in a series of formal tests of Italian. Second, C.S. and her husband were tutored in French and her acquisition was compared to that of her husband's. Third, C.S.'s ability to learn other kinds of verbal material with practice was investigated. The implications of C.S.'s apparent ability to learn a second language in the presence of a severe deficit for memory for other kinds of verbal material is discussed.

Amnesia↗
PubMed1988

Phenyl di-n-pentylphosphinate: a convenient reactivatible inhibitor for studies on neuropathy target esterase (NTE) and protection against organophosphate-induced delayed polyneuropathy.

Phenyl di-n-pentylphosphinate was synthesised by interaction of phenyl phosphorodichloridate and n-pentyl magnesium bromide. The product was purified by silica chromatography (yield 25%). Although much more stable at physiological pH than its 4-nitrophenyl analogue, this ester is a good inhibitor of neuropathy target esterase (NTE): kappa a = 1.7 X 10(5) M-1 min-1. It is a very weak anticholinesterase (kappa a congruent to 10 M-1 min-1). In vivo only 5-10 mg/kg is required to inhibit hen brain and spinal cord NTE. The inhibited NTE can be reactivated fully by incubation in vitro with iso-nitrosoacetophenone (INAP) (19 mM at 37 degrees C and pH 8.5 for 60 min): this property enables study to be made of the fate of inhibited NTE in vivo.

Animals↗
PubMed1988

More on recognition and recall in amnesics.

Hirst et al. (1986) reported that amnesic forced-choice recognition was relatively preserved when compared with amnesic recall. They equated normal recognition and amnesic recognition by extending exposure time for the amnesics and then comparing amnesic recall and normal recall. Amnesic recall was worse than normal recall, despite equated recognition. We conducted two experiments to extend that result. Experiment 1 established that the findings of Hirst et al. are not paradigm specific and hold when amnesic recognition and normal recognition are equated by increasing the retention interval for normals. In Experiment 2 we further established the generality of the result by examining yes-no recognition. Findings further specify the selective nature of the direct memory deficit in amnesics.

Amnesia↗
PubMed1988

Neuropathy target esterase: rates of turnover in vivo following covalent inhibition with phenyl di-n-pentylphosphinate.

Phenyl di-n-pentylphosphinate is a reasonably stable easily synthesized inhibitor of neuropathy target esterase (NTE) with low anticholinesterase activity. Like phenylmethylsulphonyl fluoride it protects hens against neuropathic effects of compounds such as diisopropylphosphorofluoridate. At intervals up to 15 days after dosing hens (10 mg/kg s.c. to inhibit 90% NTE) assays were made of catalytically active and of phosphinylated NTE in autopsy tissue. The sum of these components was always within the range of catalytic activity in undosed controls. However, the half-life of reappearance of active NTE was 2.07 days +/- 0.13 (SD, n = 6) for brain and 3.62 days +/- 0.23 (SD, n = 6) for spinal cord--shorter than after dosing with phenylmethylsulphonyl fluoride. It is proposed that: (1) The physiological turnover mechanism cannot distinguish between catalytically active and di-n-pentylphosphinylated NTE although initiation of organophosphate-induced delayed polyneuropathy might involve recognition of aged di-alkyl-phosphorylated NTE as "foreign". (2) The short half-lives indicate a slow spontaneous dephosphinylation of inhibited NTE occurs in vivo as well as de novo synthesis. The difference in half-lives for brain and spinal cord NTE may be due to different rates of synthesis de novo or (more likely) to different rates of spontaneous reactivation of the inhibited NTE in the two tissues.

Animals↗
PubMed1988

Phenomenal characteristics of memories for perceived and imagined autobiographical events.

Two studies explored potential bases for reality monitoring (Johnson & Raye, 1981) of naturally occurring autobiographical events. In Study 1, subjects rated phenomenal characteristics of recent and childhood memories. Compared with imagined events, perceived events were given higher ratings on several characteristics, including perceptual information, contextual information, and supporting memories. This was especially true for recent memories. In Study 2, subjects described how they knew autobiographical events had (or had not) happened. For perceived events, subjects were likely to mention perceptual and contextual details of the memory and to refer to other supporting memories. For imagined events, subjects were likely to engage in reasoning based on prior knowledge. The results are consistent with the idea that reality monitoring draws on differences in qualitative characteristics of memories for perceived and imagined events (Johnson & Raye, 1981) and augment findings from more controlled laboratory studies of complex events (Johnson & Suengas, in press; Suengas & Johnson, 1988).

Autobiographies as Topic↗
PubMed1987

Electron paramagnetic resonance and magnetic circular dichroism studies of electron-transfer flavoprotein-ubiquinone oxidoreductase from pig liver.

Pig liver electron-transfer flavoprotein-ubiquinone oxidoreductase has been investigated by room temperature UV-visible, low-temperature electron paramagnetic resonance and low-temperature magnetic circular dichroism spectroscopies. The results provide unambiguous evidence for the presence of a single [4Fe-4S] cluster that is diamagnetic in the isolated enzyme and becomes paramagnetic with an S = 1/2 ground state on reduction with dithionite or enzymatically with the physiological electron donor. The EPR data for samples at pH 7.8 indicate that FAD is reduced by one electron to the anionic semiquinone form in the enzymatically reduced enzyme, and by two electrons to the hydroquinone form by excess dithionite. The possibility of weak spin-spin interaction between the FAD semiquinone and the [4Fe-4S]1+ center is discussed in the light of the observation of a small increase in the linewidth of the Fe-S EPR in enzymatically reduced samples.

Animals↗
PubMed1987

Complete extraction in a form suitable for liquid scintillation counting of tritium-labeled proteins from polyacrylamide gels.

Large (200 mm3) slices of polyacrylamide gels crosslinked with N,N'-diallyltartardiamide which contain tritium-labeled protein are readily solubilized in periodic acid for liquid scintillation counting of radioactivity, but the apparent recovery of label never exceeds 82%. Extraction of the slices with two commercial solubilizers at 60 degrees C gave recoveries of 82-90% which were not improved by prolonged incubation. Treatment of the slices at ambient temperature with 1.0 ml of 2% sodium periodate for 30 min followed by the addition of 0.7 ml of aqueous tetrabutylammonium hydroxide (40% w/v) gives solutions which can be immediately counted at 35% efficiency with low background and with 100% recovery of tritiated protein

Electrophoresis, Polyacrylamide Gel↗
PubMed1987

Characterization of the metal clusters in the nitrogenase molybdenum-iron and vanadium-iron proteins of Azotobacter vinelandii using magnetic circular dichroism spectroscopy.

Low-temperature magnetic circular dichroism (MCD) spectroscopy has been used to investigate the metal clusters in the conventional nitrogenase MoFe protein and alternative VFe protein from Azotobacter vinelandii. In the dithionite-reduced state, the MCD spectrum of the MoFe protein is extremely similar to that previously observed for the S = 3/2 spin state of the M clusters in the MoFe protein of Klebsiella pneumoniae. A paramagnetic cluster with an S = 3/2 ground state is also responsible for the temperature-dependent MCD transitions of dithionite-reduced VFe protein. However, the electronic and magnetic properties of this cluster are quite distinct from those of M centers in conventional nitrogenase. When these proteins are oxidized with thionine, the MoFe protein exhibits MCD spectra and magnetization characteristics identical with those observed for the P clusters in K. pneumoniae, while those of the VFe protein are only similar. However, the paramagnetism in the thionine-oxidized VFe protein, like the conventional enzyme, probably arises from an S = 5/2 spin system with near-axial symmetry and a negative zero-field splitting. Novel clusters with electronic, magnetic, and redox properties similar to those of conventional P clusters are, therefore, present in the VFe protein.

Azotobacter↗
PubMed1987

Central-peripheral delayed neuropathy caused by diisopropyl phosphorofluoridate (DFP): segregation of peripheral nerve and spinal cord effects using biochemical, clinical, and morphological criteria.

Systemic injection of diisopropyl phosphorofluoridate (DFP; 1 mg/kg, sc) causes delayed neuropathy in hens. This effect is associated with a high level of organophosphorylation of neuropathy target esterase (NTE) followed by an intramolecular rearrangement called "aging." Phenylmethanesulfonyl fluoride (PMSF) also attacks the active center of NTE but "aging" cannot occur. This compound does not cause neuropathy and protects against a subsequent challenge systemic dose of DFP. Intraarterial injection of DFP (0.185 mg/kg) into only one leg of hens caused a high NTE inhibition (greater than 80%) in the sciatic nerve of the injected leg, but not in other parts of the nervous system (37% average). A unilateral neuropathy with typical histopathological lesions developed in the injected leg. PMSF (0.55 mg/kg) injected into each sciatic artery caused 47% inhibition of sciatic nerve NTE but only 17-22% inhibition of NTE elsewhere; it did not produce clinical or histopathological lesions. When these hens were challenged with DFP (1 mg/kg, sc), high inhibition of residual-free NTE (greater than 85%) occurred throughout the nervous system and clinical signs of a syndrome different from the classical delayed neuropathy developed: this spinal cord type of ataxia was associated with histopathological lesions in the spinal cord but not in peripheral nerve. PMSF (1 mg/kg) injected into only one sciatic artery caused selective protective inhibition of sciatic nerve NTE of that leg. After systemic challenge by DFP, clinical effects expressed were a combination of spinal cord ataxia plus unilateral peripheral neuropathy. The challenge dose of DFP (1 mg/kg, sc) was insufficient to produce clear histopathological lesions in unprotected peripheral nerves although spinal lesions were found in these hens. Thus clinical evaluation of the peripheral nervous system by means of walking tests and a simple test of "leg retraction" reflexes was more sensitive and specific in diagnosis of peripheral neuropathy than was the histopathology.

Animals↗
PubMed1987

The electronic and magnetic properties of rubredoxin: a low-temperature magnetic circular dichroism study.

Oxidized rubredoxin from Clostridium pasteurianum has been investigated by magnetic circular dichroism (MCD) spectroscopy over the temperature range 1.5 to 150 K and at magnetic fields between 0 and 4.5 tesla. The results show that studies of the temperature and field dependence of MCD transitions afford insight into the polarization of electronic transitions for ground states with large g-value anisotropy, in addition to estimates of ground-state g values and zero-field splitting parameters. In agreement with the assignment made by Eaton and Lovenberg (Eaton, W.A. and Lovenberg, W. (1973) in Iron-Sulfur Proteins, Vol. II (Lovenberg, W., ed.), pp. 131-162, Academic Press, New York), the ultraviolet-visible spectrum of oxidized rubredoxin is assigned to two S----Fe(III) charge transfer transitions (both 6A1----6T2 under tetrahedral symmetry), each spanning a range of 650-430 nm and 430-330 nm, respectively. The observed splitting in each of these transitions is attributed to a predominant axial distortion in the excited state resulting in effective D2d symmetry.

Circular Dichroism↗
PubMed1987

Spectroscopic studies of the seven-iron-containing ferredoxins from Azotobacter vinelandii and Thermus thermophilus.

The seven-iron-containing ferredoxins from Azotobacter vinelandii and Thermus thermophilus have been investigated by low-temperature magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR) spectroscopies and room temperature ultraviolet-visible absorption spectroscopy. The results confirm the presence of one trinuclear and one tetranuclear iron-sulfur cluster in both ferredoxins and facilitate comparison of the electronic and magnetic properties of the oxidized and reduced [3Fe-xS] clusters. MCD magnetization data are consistent with an S = 2 ground state for both reduced [3Fe-xS] clusters, but indicate differences in the rhombicity of the zero-field splittings. The data permit rationalization of the absence of a delta M = 4 EPR transition for the reduced [3Fe-xS] cluster in A. vinelandii ferredoxin I. Spectroscopic studies of anaerobically isolated A. vinelandii ferredoxin I do not support the hypothesis that the [3Fe-xS] cluster arises as a result of aerial oxidative damage to a [4Fe-4S] cluster during isolation. The possibility that two distinct forms of [3Fe-xS] clusters can exist in A. vinelandii ferredoxin I was investigated by spectroscopic studies as a function of pH. The results reveal two distinct and interconvertible forms of the reduced [3Fe-xS] cluster, but do not permit rationalization of the inconsistencies in the structural data that have been reported for the oxidized clusters.

Azotobacter↗