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Biomedical subjects

M Kumar

Publications and source records attributed to M Kumar.

At least 19 recordsLinked to original sources
PubMed1995

A methylnickel intermediate in a bimetallic mechanism of acetyl-coenzyme A synthesis by anaerobic bacteria.

Resonance Raman (RR) spectroscopy was used to identify a methylnickel adduct (upsilon Ni-C = 422 wave numbers) of carbon monoxide dehydrogenase (CODH) from Clostridium thermoaceticum. Formed at a nickel/iron-sulfur cluster on CODH called center A, the methylnickel species is the precursor of the methyl group of acetyl-coenzyme A in an anaerobic pathway of carbon monoxide or carbon dioxide fixation. Rapid kinetic and RR studies demonstrated that methylation of nickel occurs by heterolysis of the methyl-cobalt bond (upsilon Co-C = 429 wave numbers) of a methylated corrinoid/iron-sulfur protein. In combination with the earlier finding of an iron-carbonyl adduct at center A, detection of the methylnickel intermediate establishes a bimetallic mechanism for acetyl-coenzyme A synthesis.

Acetyl Coenzyme A↗
PubMed1995

The effect of phosphorylation on the antigenic reactivity of p53 in cultured human keratinocytes.

The detection of p53 in human keratinocytes is dependent on the specific anti-p53 monoclonal antibody that is used. Differences in antibody recognition are postulated to be due to the masking or exposure of particular epitopes in different conformations of p53. This study addresses the role of phosphorylation on p53-epitope accessibility in human keratinocytes. Keratinocytes were treated with the phosphatase inhibitor, okadaic acid, to determine the effect of inhibiting cellular phosphatases on p53 phosphorylation and epitope recognition. These studies suggest there is a correlation between the level of p53 phosphorylation and the antigenic reactivity of certain p53 epitopes in human keratinocytes. We also examined the ability of the catalytic subunits of protein phosphatase 1 and 2A to dephosphorylate p53 derived from human keratinocytes in vitro. These data suggest that PP2A may be the phosphatase that acts on p53 in cultured human keratinocytes.

Antibodies, Monoclonal↗
PubMed1995

Nocturnal/daytime urine noradrenergic measures and sleep in combat-related PTSD.

Prominent heightened arousal symptoms and clinical/laboratory findings implicate the central noradrenergic system in posttraumatic stress disorder (PTSD). Heightened arousal frequently manifests in relation to sleep in PTSD. Central noradrenergic systems have a role in regulating arousal levels during sleep. We therefore evaluated noradrenergic production via urinary excretion in relation to sleep/wake activity in PTSD patients and controls. Twenty patients--all Vietnam veterans diagnosed with combat-related PTSD--and eight non-ill, non-combat-exposed controls had overnight sleep studies under medication and substance-free conditions. In association with sleep recording, subjects saved their urine for 24 hours in three 8-hour collections in order to obtain "daytime" (8:00 AM to 4:00 PM, 4:00 PM to MN) and "nocturnal" (MN to 8:00 AM) catecholamine measures. PTSD patients had decreased sleep efficiency relative to controls and increased REM density; 24-hour norepinephrine and MHPG (the more centrally derived metabolite) did not differ between patients and controls. "Nocturnal" excretion of MHPG minus the average of the two "daytime" values was negative in the controls, slightly positive in the patients, and differed significantly between the two groups. "Nocturnal minus daytime" MHPG also correlated negatively with total sleep time in the PTSD patients (R = -.45, p < .05). Our data support a relationship of nondiminished central noradrenergic activity at night, and sleep disturbance, in chronic, combat-related PTSD.

Adult↗
PubMed1995

Mechanism of CO oxidation by carbon monoxide dehydrogenase from Clostridium thermoaceticum and its inhibition by anions.

Carbon monoxide dehydrogenase (CODH) performs two distinct reactions at two different metal centers. The synthesis of acetyl-CoA from a methyl group, CO, and coenzyme A occurs at center A and the oxidation of CO to CO2 occurs at center C. In the work reported here, we have studied the mechanism of CO oxidation by CODH and its inhibition by thiocyanate. Our data are consistent with a ping-pong mechanism. A scheme to explain the first half-reaction was developed that includes binding of water and CO to the oxidized form of center C, deprotonation of coordinated water to yield enzyme-bound hydroxyl, nucleophilic attack on coordinated CO by OH- to form enzyme-bound carboxyl, and deprotonation and decarboxylation to form CO2 and the reduced form of center C. In the second half-reaction, the reduced enzyme is reoxidized by an electron acceptor. CO oxidation was pH dependent. The pH dependence of kcat/Km for CO gave a single pKa of 7.7 and a maximum value at 55 degrees C and high pH of 9.1 x 10(6) M-1 s-1. The pH dependence of kcat followed a two-phase titration curve with pKa values of 7.1 and 9.5 and maximum value of kcat at 55 degrees C and high pH of 3250 s-1 (1310 mumol of CO oxidized min-1 mg-1). The pH dependencies of kcat/Km and kcat are interpreted to reflect the ionization of enzyme-bound water from binary and ternary complexes with center C. Reaction with thiocyanate, azide, or cyanate was found to cause a striking shift in the EPR spectrum of center C from gav = 1.82 (g = 2.01, 1.81, 1.65) to a two-component spectrum with gav = 2.15 (g = 2.34, 2.067, 2.03) and gav = 2.17 (g = 2.34, 2.115, 2.047). Thiocyanate acted as a mixed partial inhibitor with respect to CO. The inhibition constants were pH and temperature dependent. The pH dependencies of the inhibition constants gave pKa values of approximately 7.7. Binding of thiocyanate to the oxidized form of center C appears to be favored by a negative enthalpy that is offset by a decrease in entropy yielding a slightly unfavorable free energy of association.

Aldehyde Oxidoreductases↗
PubMed1995

Structural and electronic factors in heterolytic cleavage: formation of the Co(I) intermediate in the corrinoid/iron-sulfur protein from Clostridium thermoaceticum.

We have completed the first direct structural characterization of an enzyme-bound four-coordinate Co(I) intermediate, in this case for the corrinoid/iron-sulfur protein (C/Fe-SP) from Clostridium thermoaceticum. Extended X-ray absorption fine structure and X-ray edge spectroscopy of the active Co(I) state of the C/Fe-SP indicates a four-coordinate (distorted) square-planar structure where the best fit gives average Co-N(equatorial) distances of 1.87 +/- 0.01 A, corresponding to 4.2 +/- 0.3 ligands. The X-ray edge spectrum of Co(I) C/Fe-SP contains a moderate intensity 1s-4p + "shake-down" (SD) transition and no 1s-3d peak (where SD transitions are indicative of square-planar geometries). X-ray edge results for the methyl-Co(III) form, reported earlier [Wirt, M. D., Kumar, M., Ragsdale, S. W., & Chance, M. R. (1993) J. Am. Chem. Soc. 115, 2146-2150], are consistent with a base-off methylcobamide structure. The absence of a ligated 5-methoxybenzimidazole base in the methyl-Co(III) state is important since the base-off form is predicted to predispose the Co-C bond toward heterolytic cleavage to form the four-coordinate Co(I) species concurrent with methyl transfer. Additionally, we have examined first-derivative X-ray edge spectra of Co(I) C/Fe-SP, relative to edge spectra of a cobalt foil, as an indicator of effective nuclear charge on cobalt. The Co(I) C/Fe-SP edge position at 7720.5 +/- 0.3 eV is less than, but very close to, the value seen for the corresponding free Co(I) cobalamin.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Proteins↗
PubMed1995

Infants with metastatic neuroblastoma have improved survival with resection of the primary tumor.

Although infants (age less than 1 year) with neuroblastoma have a favorable overall prognosis, metastatic disease is associated with poorer treatment outcome. To assess the role of surgery in these patients, the authors reviewed survival data for 151 infants treated for neuroblastoma, focusing on patient and tumor characteristics, biological markers, and surgical management among the 99 patients with metastatic disease. Patients were divided into early (1961 to 1978) and contemporary (1979 to 1993) treatment eras. Potential prognostic factors were statistically tested to determine their significance in affecting survival. Five-year survival by Pediatric Oncology Group stage was: A, 100% (+/- 0%); B, 94% (+/- 6%); DS, 77% (+/- 9%); C, 73% (+/- 9%); and D, 61% (+/- 8%). Survival for infants with metastatic disease (stages C, D, and DS) was affected significantly by treatment era (P = .0001). Analyses restricted to patients treated during the contemporary era showed prognostic significance for DNA index (P = .02), N-myc copy number (P = .007), serum lactate dehydrogenase level (P = .001), and extent of resection (P = .01). A > or = 95% resection of the primary tumor was found to be associated with improved survival. Significantly more surgical complications were associated with resections performed at the time of diagnosis (P = .007), and delaying surgery until after several courses of chemotherapy did not decrease survival. In conclusion, multiple factors affect the outcome of treatment for infants with metastatic neuroblastoma, and whenever feasible, a > or = 95% resection of the primary tumor should be performed in this patient subgroup.

Biomarkers↗
PubMed1995

Comparison of fresh and glutaraldehyde-treated autologous stented pericardium as pulmonary valve replacement.

The use of fresh autologous pericardium in valve surgery has shown poor results in the past mainly due to thickening and retraction. Recently, it has been suggested that a short treatment with glutaraldehyde might radically change its behavior. In an attempt to determine whether this disparity in results is due to the glutaraldehyde treatment or to a better present-day surgical technique, fresh and glutaraldehyde-treated autologous pericardium was mounted in a frame and implanted in the pulmonary position of adult sheep. Six survivors obtained in each group were sacrificed between 2 and 8 months in the "fresh" group and between 2 and 6 months in the "glutaraldehyde-treated" group. Macroscopically, the fresh pericardium became thickened and retracted in all specimens, eventually resulting in severe regurgitation, while the glutaraldehyde-treated, although slightly thickened, retained its pliability without significant retraction. Microscopically, viability of the central core of the collagen was more often preserved in the fresh pericardium. Endothelialization was irregular. In conclusion, short glutaraldehyde treatment seems to improve the results of autologous pericardium mounted on a valve stent. Its effect on calcification remains to be ascertained.

Animals↗
PubMed1995

Peripheral serotonin in Alzheimer's disease.

The platelet has been suggested to be a peripheral model of the central serotonergic neuron. This investigation was carried out in order to test the hypothesis that levels of serotonin (5-HT) in the platelet will be decreased in Alzheimer's disease (AD) since neurochemical studies suggest that levels of 5-HT are decreased in the brain of AD patients. We investigated platelet and plasma 5-HT in a group of AD patients (n = 22) as well as in age-matched normal control subjects (n = 20). The results show that the platelet level of 5-HT was significantly reduced in AD (65.7 +/- 28.41 ng/10(8) platelets in AD vs. 112.9 +/- 35.11 ng/10(8) platelets in controls; p = 0.0001). There was no effect on the levels of its metabolite 5-hydroxyindoleacetic acid. These findings suggest that the peripheral serotonergic system in AD is adversely affected.

Aged↗
PubMed1995

A revised terminology for recording surgical findings of the mitral valve.

The existing terminology for the various structures of the mitral valve are diverse and numerous. With the resurgence of interest in reparative procedures for mitral valve disease, it becomes imperative to have a unified terminology which would convey precise connotations in recording the pathology as well as the corrective procedures applied. In an effort to suggest a commonly acceptable nomenclature, we reviewed the available terminology and propose a simple system which will fulfil the needs of recording the intraoperative observations of the pathology of each valve and the manouveres carried out to correct them by the surgeon. This involves designating all structures anterior to the intercommissural line as "anterior" or "A" and those posterior as "posterior" or "P". The structures, as observed by the surgeon through a standard left atriotomy, to the left of the line dropped perpendicular to the middle of the aortic curtain will be designated by the numeral "1" and those to the right "2". The chords will be termed in groups based on their point of insertion, irrespective of whether they are inserted to the free edge or the ventricular surface of the leaflet. The anterior leaflet chords will further be subdivided based on their relation to the stay chords. We hope that this system of naming the structures would provide a unified method of reporting intraoperative findings of mitral valve disease.

Heart Valve Diseases↗
PubMed1994

Binding of carbon disulfide to the site of acetyl-CoA synthesis by the nickel-iron-sulfur protein, carbon monoxide dehydrogenase, from Clostridium thermoaceticum.

Carbon monoxide dehydrogenase (CODH) is a key enzyme in the pathway of carbon monoxide and carbon dioxide fixation by anaerobic bacteria. It performs the oxidation of CO to CO2, the reduction of CO2 to CO, and the synthesis of acetyl-CoA from a methylated corrinoid/iron-sulfur protein, CO, and CoA. These reactions occur at metal centers on CODH and involve metal-carbon bond formation and transformation. There are three iron-containing centers that play distinct roles in CODH: Centers A, B, and C. Center A is the site of synthesis of acetyl-CoA and catalyzes an exchange reaction between CO and acetyl-CoA. Center C is the site of CO oxidation and CO2 reduction. In the work described here, inhibition of CODH by carbon disulfide was studied. CS2 was found to serve as a probe of the interaction of CODH with CO at Center A. EPR spectroscopic and steady-state kinetic studies demonstrated that CS2 mimics the binding of CO to the nickel/iron-sulfur cluster at Center A; however, CS2 itself does not undergo oxidation-reduction and does not appear to bind to Center C as does CO. In the isotope exchange reaction between acetyl-CoA and CO, CS2 was found to be a competitive inhibitor with respect to CO (Ki = 0.47 mM) and a mixed inhibitor with respect to acetyl-CoA (Ki1 = 0.30 and Ki2 = 1.1 mM). The reaction of dithionite-reduced CODH with CS2 resulted in an EPR spectrum with g values of 2,200, 2,087, and 2,017.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetyl Coenzyme A↗
PubMed1994

Nature's carbonylation catalyst: Raman spectroscopic evidence that carbon monoxide binds to iron, not nickel, in CO dehydrogenase.

Carbon monoxide dehydrogenase catalyzes the synthesis of acetyl-coenzyme A from coenzyme A, a methyl group, and carbon monoxide. The carbon monoxide binds to a mixed metal center of the enzyme, which contains nickel bridged to an iron-sulfur cluster. Resonance Raman spectroscopy has been used to identify both C-O stretching and metal-CO stretching vibrations of the carbon monoxide adduct of the enzyme. This adduct was shown by isotopic exchange to be on the pathway for acetyl-coenzyme A synthesis. The metal to which carbon monoxide is bound was established to be iron, not nickel, by preparation of enzyme from bacteria grown on iron-54 and nickel-64. The Fe-CO frequency is low, 360 wave numbers, implying a weak bond, probably because of electron donation from sulfide and thiolate ligands of the iron. A bimetallic mechanism is proposed, in which carbon monoxide binds to an iron atom and is subsequently attacked by a methyl group on a nearby nickel atom, forming an acetyl ligand, which is then transferred to coenzyme A.

Acetyl Coenzyme A↗
PubMed1994

Congenital coagulopathies and pregnancy: report of four pregnancies in a factor X-deficient woman.

Pregnancy in women with congenital coagulation factor deficiencies has been associated with adverse fetal outcomes. Recurrent spontaneous abortions, placental abruptions, and premature births are reported, the exact reasons for which are not clear, and management of such patients continues to be a challenge. We reviewed the outcome of four pregnancies in a patient with factor X deficiency, and looked at the effect of factor replacement therapy on pregnancy. Her first two pregnancies resulted in the birth of extremely premature babies at 21 and 25 weeks of gestation, both of which died in the neonatal period. The patient was treated with fresh frozen plasma for acute bleeding episodes during these pregnancies. In addition during her second conception she was given factor IX complex [Konyne] prophylactically, but only in the latter half of her pregnancy. During her next two pregnancies she was treated early on during pregnancy, with prophylactic replacement of factor X. She delivered healthy babies at 34 and 32 weeks of gestation, and they are both doing well. We therefore suggest possible mechanisms by which aggressive prophylactic factor support in a female with severe congenital coagulopathy, may improve on fetal outcome.

Adult↗
PubMed1994

Changes in cognitive coping strategies predict EBV-antibody titre change following a stressor disclosure induction.

Previous research has shown that emotional disclosure of traumatic or stressful events is associated with facilitating insight into the experience, improving mood, and modulating some aspects of the immune system. The current study examined how cognitive changes and experiential involvement during an emotional disclosure induction protocol relate to immune functioning, as measured by IgG antibody titres to the Epstein-Barr virus viral capsid antigen (EBV-VCA). Seventy-six college undergraduates were randomly assigned to either a disclosure induction or an assessment-only control condition. Experimental subjects met with an experimenter for three weekly 20-min individual sessions during which time they were asked to discuss a stressful or traumatic topic which they had previously discussed only minimally with others. Blood was drawn a week prior to the first session and at one week following the third session. Subjects completed the Impact of Event Scale (IES) after session 1 and at followup, and the extent of experiential involvement in disclosure during each session was assessed by means of the Experiencing Scale. Mood was assessed before and after each disclosure using the Nowlis Mood Adjective Checklist. Although the disclosure induction did not directly affect EBV-VCA antibody titres, individual differences in subjects' ability to involve themselves in the disclosure process and abandon their avoidance of the stressful tropic during the course of the 3-wk period were predictive of antibody decrements. These associations were more pronounced for individuals who disclosed older and more troublesome events.

Adaptation, Psychological↗
PubMed1994

Monitoring intrathecal temperature: does core temperature reflect intrathecal temperature during aortic surgery?

Paraplegia secondary to spinal cord ischemia is a common occurrence following proximal aortic surgery. Recent research has suggested that modest reductions in neuronal temperature (ie, a 2 to 5 degrees C reduction) may protect the central nervous system from ischemic injury, and several medical centers are now using modest whole body hypothermia in an attempt to protect the spinal cord during aortic surgery. However, to date, there are no reports to validate that reductions in core temperature will reduce intrathecal temperature during aortic surgery. In the present study, the correlation between core temperature, assessed with a pulmonary artery thermistor, and intrathecal temperature, assessed with a lumbar intrathecal thermocouple, were evaluated. Both devices were corrected for bias using a mercury thermometer standard. It was found that there was excellent correlation between pulmonary artery temperature and intrathecal temperature during all portions of the surgery (r = 0.948; P < 0.001). The regression line for the relationship was defined by the formula: intrathecal temperature = 0.98 x pulmonary artery temperature + 0.65. Furthermore, there was excellent correlation between bias-corrected intrathecal temperature and the temperature measured by commercially available, bias-uncorrected thermistors placed in the esophagus (r = 0.869; P < or = 0.001), urinary bladder (r = 0.873; P < 0.001), and pulmonary artery (r = 0.929; P < 0.001). Based on these data, it is concluded that there is a close correlation between intrathecal temperature and core temperatures during proximal aortic surgery, and commercially available thermistors provide sufficient accuracy to assess spinal cord cooling during attempts to protect the spinal cord from ischemic injury.

Aortic Aneurysm, Abdominal↗
PubMed1994

Cerebrospinal fluid dopamine in HIV-1 infection.

BACKGROUND: Increasing evidence suggests significant involvement of the basal ganglia in patients with HIV-1 infection. OBJECTIVE: To study the effect of HIV-1 infection on cerebrospinal fluid (CSF) dopamine levels. DESIGN: CSF dopamine levels were measured by high-performance liquid chromatography. SETTING: A university-based outpatient clinic in south Florida involved in clinical AIDS research. SUBJECTS: Twenty-two subjects were enrolled in a prospective, longitudinal study of the neurological complications of AIDS. Five subjects were HIV-seronegative, but at risk for HIV-1 infection, 11 were HIV-1-seropositive without neurological disease and six had HIV-1-related neurological disease. RESULTS: The CSF dopamine mean values were significantly lower in the HIV-1-seropositive group with (P < 0.0001) or without (P < 0.0001) neurological disease than in the HIV-seronegative group. There was a very strong correlation between CD4 lymphocyte counts and CSF dopamine levels (P = 0.004) in the neurologically symptomatic group (P = 0.0008), but not in the other two groups. CONCLUSION: HIV-1 infection appears to have an effect on the central nervous system dopaminergic systems, as reflected in levels of CSF dopamine.

Adult↗