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Biomedical subjects

M Good

Publications and source records attributed to M Good.

68 records · Page 4Linked to original sources
PubMed1986

Iron(II)-substituted metallothionein: evidence for the existence of iron-thiolate clusters.

Metallothioneins (MT's) are unique low molecular weight (Mr 6000-7000) metal- and cysteine-rich proteins characterized by two tetrahedral tetrathiolate clusters containing three and four metal ions. Naturally occurring proteins usually contain the diamagnetic metal ions Zn(II) and/or Cd(II). We have now succeeded in substituting these ions by paramagnetic Fe(II). Rabbit liver MT-1 in which all seven metal binding sites were occupied by Fe(II) ions displays absorption features typical of tetrahedral tetrathiolate Fe(II) coordination. This is documented by the presence of a ligand field 5E----5T2 transition in the near-infrared region centered at about 1850 nm (epsilon Fe approximately 100 M-1 cm-1) and a broad charge-transfer absorption in the UV region with a shoulder at 314 nm. A metal-thiolate cluster structure is inferred from the 7 to 20 ratio of metal ions to cysteine residues and from spectral studies in which successive increments of Fe(II) were incorporated into the metal-free protein. Thus, to about 4 equiv, the charge-transfer absorption and magnetic circular dichroism (MCD) features of the complexes formed resemble closely those of reduced rubredoxin from Desulfovibro gigas in which tetrahedral tetrathiolate Fe(II) coordination is documented. However, upon further addition of Fe(II) ions, the charge-transfer absorption bands undergo a progressive red-shift until the full metal occupancy of seven Fe(II) ions per molecule is reached. The bathochromic shift which is also manifested in the MCD spectra can be ascribed to the transformation of some of the terminal thiolate ligands to bridging when the full complement of Fe(II) is bound.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Spectroscopic properties of the cobalt(II)-substituted alpha-fragment of rabbit liver metallothionein.

The C-terminal segment of rabbit liver metallothionein 1 (alpha-fragment) containing four paramagnetic Co(II) ions was obtained by stoichiometric replacement of the originally bound diamagnetic Cd(II) ions. The latter form was prepared by limited proteolysis with subtilisin as described previously [Winge, D. R., & Miklossy, K. A. (1982) J. Biol. Chem. 257, 3471-3476]. Electronic absorption, magnetic circular dichroism (MCD), and electron paramagnetic resonance (EPR) measurements were employed to monitor the stepwise incorporation of Co(II) ions into the metal-free fragment. Absorption and MCD spectra of the apofragment containing the first 3 Co(II) equiv show the typical features of tetrahedral tetrathiolate Co(II) coordination. However, in the d-d region only small changes in the visible and no apparent change in the near-infrared region are discernible when the fourth Co(II) is bound. This unusual spectral behavior was not seen in Co(II) substitution of native metallothionein [Vasák, M., & Kägi, J. H. R. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6709-6713] and may indicate a different cluster geometry. In the charge-transfer region, the binding of all 4 Co(II) equiv is accompanied by characteristic increments of the thiolate S----Co(II) bands. As in the formation of Co(II)7-metallothionein, the development of the charge-transfer and EPR spectral properties upon binding of the first 2 Co(II) equiv to the apofragment is indicative of isolated, noninteracting tetrahedral tetrathiolate Co(II) complexes. The binding of the additional Co(II) ion is accompanied by a red shift in the charge-transfer region and by the dramatic loss of paramagnetism in the EPR spectra, both diagnostic of the formation of metal-thiolate cluster structures.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗
PubMed1984

Structure of mammalian metallothionein.

All mammalian metallothioneins characterized contain a single polypeptide chain of 61 amino acid residues, among them 20 cysteines providing the ligands for seven metal-binding sites. Native metallothioneins are usually heterogeneous in metal composition, with Zn, Cd, and Cu occurring in varying proportions. However, forms containing only a single metal species, i.e., Zn, Cd, Ni, Co, Hg, Pb, Bi, have now been prepared by in vitro reconstitution from the metal-free apoprotein. By spectroscopic analysis of such derivatives it was established that all cysteine residues participate in metal binding, that each metal ion is bound to four thiolate ligands, and that the symmetry of each complex is close to that of a tetrahedron. To satisfy the requirements of the overall Me7(Cys-)20 stoichiometry, the complexes must be combined to form metal-thiolate cluster structures. Experimental proof for the occurrence of such clusters comes from the demonstration of metal-metal interactions by spectroscopic and magnetic means. Thus, in Co(II)7-metallothionein, the Co(II)-specific ESR signals are effectively suppressed by antiferromagnetic coupling of juxtaposed paramagnetic metal ions. By monitoring changes in ESR signal size occurring on stepwise incorporation of Co(II) into the protein, it is possible to follow the building up of the clusters. This process is biphasic. Up to binding of four equivalents of Co(II), the ESR amplitude increases in proportion to the metal content, indicating generation of magnetically noninteracting high-spin complexes. However, upon addition of the remaining three equivalents of Co(II), these features are progressively suppressed, signaling the formation of clusters. The same mode of cluster formation has also been documented for Cd and Hg. The actual spatial organization of the clusters and the polypeptide chain remains to be established. An attractive possibility is the arrangement of the tetrahedral metal-thiolates in adamantane-like structures surrounded by properly folded segments of the chain providing the ligands. 1H-NMR data and infrared absorption measurements are consistent with a tightly folded structure rich in beta-type conformation.

Amino Acid Sequence↗
PubMed1981

Sensitivity and resistance of human melanoma cells to ultraviolet radiation.

A human melanoma cell line (MM253) was found to be sensitive to ultraviolet (UV) radiation, having a Do of 1.0 J/M2 when cloned on plastic culture dishes and a Do of 2.3 J/m2 when cloned in agar. These figures are much lower than those obtained for all other human melanoma cell lines studied in this laboratory (Do of 32-40 J/m2) and demonstrate that MM253 is unusually UV sensitive. The increased level of UV sensitivity in MM253 is not due to a reduced capacity for excision of pyrimidine dimers, repair of DNA single-strand breaks or elongation of newly-synthesized DNA strands when comparison is made with a UV-resistant melanoma cell line.

Cell Line↗
PubMed1978

Dependence on cloning method of survival of human melanoma cells after ultraviolet and ionizing radiation.

The resistance of a human melanoma cell line (MM96) to both ultraviolet and ionizing irradiation was compared by two different methods of cloning, on plates and in agar. A high level of resistance to both ultraviolet (D0 = 320 ergs/sq mm) and ionizing irradiation (D0 = 4300 rads) was observed when viability of cells was determined by cloning in agar. In contrast, melanoma cells were found to be as sensitive as were other cells when viability after irradiation was determined by cloning on plastic plates. The difference in sensitivity to radiation between the two methods of cloning can be explained in a model involving damage to membranes as well as to DNA. At least for ionizing radiation, this effect is not restricted to melanoma cells since a HeLa subline, HeLa-QB1, showed a similar response. In contrast, a human lymphoblastoid line (JHP) cloned in agar was sensitive under these conditions (D0 = 120 rads).

Agar↗
PubMedDate not supplied

The effects of hippocampal-area parahippocampalis lesions on discrimination learning in the pigeon.

Three experiments examined the behavioural effects of bilateral ablation of the avian hippocampus-area parahippocampalis (Hp-APH), a region which is considered to be the homologue of the mammalian hippocampal formation. Pigeons with lesions of the Hp-APH were impaired in learning the reversal (but not the acquisition) of a position (left/right) discrimination (Expt. 1). In contrast, lesion birds were unimpaired relative to controls in both the acquisition and reversal of a visual (pattern) discrimination (Expt. 2) in terms of errors to criterion; there was evidence, however, that the pattern of responding differed between groups during reversal. Finally, Hp-APH pigeons were impaired in the acquisition of a conditional discrimination (Expt. 3). The results are compared with the effects of hippocampal ablation in mammals, and their implications for a behavioural homology between the avian Hp-APH and the mammalian hippocampal formation are considered.

Animals↗
PubMedDate not supplied

Enhanced DRL and impaired forced-choice alternation performance following hippocampal lesions in the pigeon.

In four experiments, pigeons with bilateral lesions of the hippocampus were compared to unoperated control birds and operated control subjects that received bilateral lesions of the neostriatum on tasks sensitive to hippocampal damage in mammals. Consistent with the mammalian literature, hippocampal birds were impaired on forced-choice alternation in the T-maze, although they were unimpaired on spatial alternation and reversal learning in an operant chamber. Furthermore, in contrast to hippocampal mammals, hippocampal pigeons showed enhanced performance on a differential reinforcement of low-rates of responding schedule of reinforcement. The results are discussed with respect to a behavioural homology between the avian and mammalian hippocampal formations.

Animals↗
PubMedDate not supplied

Management of a patient with insulin-dependent diabetes mellitus learning biofeedback-assisted relaxation.

Psychological stress can have profound disruptive effects upon glycemic control in individuals with diabetes. Presented here is a case study in which biofeedback-assisted relaxation techniques were used to help a young woman with a 10-year history of insulin-dependent diabetes mellitus to more effectively manage stress, thereby improving glycemic control. Hypoglycemia is a frequently encountered problem with this technique, so the patient was taught to identify causes of hypoglycemic episodes and to take action to prevent their occurrence. The team approach of a diabetes nurse educator working in conjunction with a biofeedback therapist was vital to the success of this program.

Adult↗
PubMedDate not supplied

Pain outcomes after intestinal surgery.

Pain sensation and distress in 38 intestinal surgical patients were moderate to severe on postoperative day 1, ranging from 34 to 49 mm and 33 to 45 mm, respectively, on 100-mm scales. During ambulation, both increased from baseline to post-ambulation, P < 0.01. Half of the patients reported severe pain not relieved by analgesics, and although 44% learned a relaxation technique in the past, only 8% used one for pain after this surgery. Pain disturbed the sleep of 34% of the patients, and pain was related to respiratory, intestinal, febrile, and other complications in 18 (47%) subjects. Attentive analgesic use and nonpharmacologic therapies are recommended.

Adult↗
PubMedDate not supplied

A comparison of the effects of jaw relaxation and music on postoperative pain.

This experimental study compared the effects of jaw relaxation and music, individually and combined, on sensory and affective pain following surgery. Abdominal surgical patients (N = 84) were randomly assigned to four groups: relaxation, music, a combination of relaxation and music, and control. Interventions were taught preoperatively and used by subjects during the first ambulation after surgery. Indicators of the sensory component of pain were sensation and 24-hour narcotic intake. Indicators of the affective component of pain were distress and anxiety of pain. With preambulatory sensation, distress, narcotic intake, and preoperative anxiety as covariates, the four groups were compared using orthogonal a priori contrasts and analysis of covariance. The interventions were neither effective nor significantly different from one another during ambulation. However, after keeping the taped interventions for 2 postoperative days, 89% of experimental subjects reported them helpful for sensation and distress of pain.

Adult↗