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H C Lee

Publications and source records attributed to H C Lee.

At least 19 recordsLinked to original sources
PubMed1995

Electron spin echo envelope modulation study of oxygenated iron-cobalt hybrid hemoglobins reveals molecular features analogous to those of the oxy ferrous protein.

Two oxygenated iron-cobalt hybrid hemoglobins (Hbs), (alpha Co-O2 beta Fe-O2)2 and (alpha Fe-O2 beta Co-O2)2, were studied by electron spin echo envelope modulation (ESEEM) spectroscopy in order to measure (i) electron-nuclear hyperfine and nuclear quadrupole coupling to the N epsilon of the proximal histidyl imidazole and (ii) nuclear hyperfine coupling to exchangeable 2H in the oxyCo subunits. 14N couplings were found to be smaller in the oxyCo alpha subunits than in the oxyCo beta subunits, suggesting a more ionic and shorter Co-O2 bond in the alpha subunits [Lee et al. (1994) Biochemistry 33, 7609], which correlates with the higher O2 affinity found for (alpha Co beta Fe-O2)2 Hb than for (alpha Fe-O2 beta Co)2 Hb [Imai et al. (1980) J. Mol. Biol. 138, 635]. A smaller nuclear quadrupole coupling constant found for the proximal histidyl N epsilon in the oxyCo alpha subunits also suggests an increase in the overlap between the N epsilon sp2 hybrid and the Co dz2 orbital, i.e., a shorter Co-N epsilon bond, than in the oxyCo beta subunits. On the other hand, the relative orientation of the g and 14N epsilon nuclear quadrupole tensors, obtained by spectral simulation, suggests that the Co-O-O bond angle is similar in the two types of oxyCo subunits. An X-ray crystallographic study of oxyFe Hb A [Shaanan, B. (1982) Nature 296, 683] has also reported similar Fe-O-O bond angles in both alpha and beta subunits, but with shorter Fe-N epsilon and Fe-O2 bonds in the alpha subunits.(ABSTRACT TRUNCATED AT 250 WORDS)

Cobalt↗
PubMed1995

Sensitization of calcium-induced calcium release by cyclic ADP-ribose and calmodulin.

Cyclic ADP-ribose (cADPR) is emerging as an endogenous regulator of Ca2+-induced Ca2+ release (CICR), and we have recently demonstrated that its action is mediated by calmodulin (CaM) (Lee, H. C., Aarhus, R., Graeff, R., Gurnack, M. E., and Walseth, T. F. (1994) Nature 370, 307-309). In this study we show by immunoblot analyses that the protein factor in sea urchin eggs responsible for conferring cADPR sensitivity to egg microsomes was CaM. This was further supported by the fact that bovine CaM was equally effective as the egg factor. In contrast, plant CaM was only partially active even at 10-20-fold higher concentrations. This exquisite specificity was also shown by binding studies using 125I-labeled bovine CaM. The effectiveness of various CaMs (bovine > spinach > wheat germ) in competing for the binding sites was identical to their potency in conferring cADPR sensitivity to the microsomes. A comparison between bovine and wheat germ CaM in competing for the sites suggests only 10-14% of the total binding was crucial for the activity. Depending on the CaM concentration, the sensitivity of the microsomes to cADPR could be changed by several orders of magnitude. The requirement for CaM could be alleviated by raising the divalent cation concentration with Sr2+. Results showed that CaM, cADPR, and caffeine all act synergistically to increase the divalent cation sensitivity of the CICR mechanism. The combined action of any of the three agonists was sufficient to sensitize the mechanism so much that even the nanomolar concentration of ambient Ca2+ was enough to activate the release. Unlike the CICR mechanism, the microsomal inositol 1,4,5-trisphosphate-sensitive Ca2+ release showed no dependence on CaM. Using an antagonist of CaM, W7, it was demonstrated that the cADPR-but not the inositol 1,4,5-trisphosphate-dependent release mechanism could be blocked in live sea urchin eggs. These results indicate cADPR can function as a physiological modulator of CICR and, together with CaM, can alter the sensitivity of the release mechanism to divalent cation by several orders of magnitude.

Adenosine Diphosphate Ribose↗
PubMed1995

Drosophila glutathione S-transferase D27: functional analysis of two consecutive tyrosines near the N-terminus.

The Drosophila glutathione S-transferase D27 (GST D27) has been purified and characterized after direct expression of the intronless gstD27 gene in E. coli. The GST D27 has both conjugation activity against the common substrate 1-chloro-2,4-dinitrobenzene and peroxidase activity against cumene hydroperoxide. Its pH optimum is 8.5 in 0.125 M bis-tris propane buffer at 22 degrees C. It is more thermal labile than the human GST121. The GST D27 has two tyrosines at positions 3 and 4. Both of them appear to be important but neither of them is essential for the enzyme activity. Thus, other residues may also participate in catalysis. The two tyrosines of GST D27 could also be important in binding to GSH or S-hexyl GSH. Results from in vitro biochemical analyses were confirmed by the in vivo activity-based CDNB growth inhibition analyses. Our results clearly indicate that the Drosophila GST D isozymes are different from any of the known mammalian GSTs.

Animals↗
PubMed1995

Caged cyclic ADP-ribose. Synthesis and use.

Cyclic ADP-ribose (cADPR) is a recently discovered cyclic nucleotide with Ca2+ mobilizing activity. Caged cADPR was synthesized by reacting cADPR with 2-nitrophenethyldiazoethane. Elemental analyses, 1H NMR, and extinction coefficient measurements indicate that the product contains only one caging group. Anion exchange high pressure liquid chromatography separated caged cADPR into two forms, which most likely represent isomers. Both forms could be uncaged with equal efficiency by UV exposure to regenerate cADPR. Photolysis of caged cADPR was accomplished effectively with a spectrofluorimeter. The efficiency of uncaging depended on wavelength with UV light shorter than about 320 nm being the most effective. Caged cADPR was biologically inactive and could induce Ca2+ release from sea urchin egg homogenates only after photolysis. Specificity of the Ca2+ release was shown by inhibition by 8-amino-cADPR, a specific antagonist of cADPR. To demonstrate its utility in live cells, caged cADPR was microinjected into sea urchin eggs. Photolysis using a mercury light source effectively regenerated cADPR and resulted in Ca2+ mobilization and activation of cortical exocytosis in the eggs.

ADP-ribosyl Cyclase↗
PubMed1995

Functional expression of soluble forms of human CD38 in Escherichia coli and Pichia pastoris.

Cyclic adenosine diphosphate (ADP)-ribose (cADPR), a metabolite of nicotinamide adenine dinucleotide (NAD+), mobilizes calcium from intracellular stores in many cells. The synthesis of cADPR from NAD+ and its subsequent hydrolysis to ADPR is catalyzed by an ADP-ribosyl cyclase and a cADPR hydrolase, respectively. The ADP-ribosyl cyclase cloned from the ovotestis of the marine invertebrate Aplysia californica has amino acid sequence homology to the human lymphocyte surface antigen CD38. CD38 has been shown to catalyze both the formation and the hydrolysis of cADPR. In this study, we produced soluble, enzymatically active CD38 using recombinant expression techniques in bacteria and yeast. We engineered a gene coding for a soluble form of CD38 by excision of the region of the gene coding for the N-terminal amino acids representing the putative membrane spanning sequence and short putative intracellular sequence. For expression in bacteria (Escherichia coli), this construct was cloned into the pFlag-1 plasmid which allows induced, periplasmic expression and relatively simple purification of the soluble CD38. For expression in yeast (Pichia pastoris) the CD38 sequence was further modified to eliminate four putative N-linked glycosylation sites and the resulting construct was expressed as a secreted protein. Both systems produce soluble enzymes of approximately 30 kDa and both recombinant enzymes display similar cyclase and hydrolase activities.

ADP-ribosyl Cyclase↗
PubMed1995

Acipimox potentiates growth hormone response to growth hormone-releasing hormone by decreasing serum free fatty acid levels in hyperthyroidism.

Hyperthyroidism is associated with an impairment of growth hormone (GH) responses to secretagogues. The aim of this study was to evaluate the effect of acipimox, an antilipolytic agent able to decrease free fatty acids (FFA), on GH response to GH-releasing hormone (GHRH) in hyperthyroid and normal control subjects. We studied six men with hyperthyroidism; seven normal men served as control subjects. Each subject underwent treatment with (1) 2 tablets of placebo orally or (2) 500 mg acipimox orally, 120 minutes before intravenous (IV) injection of 1 microgram/kg GHRH-(1-29)NH2. GH response to GHRH in hyperthyroid patients was markedly reduced; the mean peak GH response (9.6 +/- 1.0 microgram/L) and the area under the GH response curve (12.9 +/- 1.3 micrograms/L x 2 h) were lower than those of control subjects (25.7 +/- 1.8 micrograms/L, P < .05; 28.7 +/- 2.1 micrograms/L x 2 h, P < .05). Hyperthyroid patients had higher baseline levels of plasma FFA than control subjects (998.0 +/- 38.9 v 498.0 +/- 36.0 muEq/L, P < .01). Acipimox decreased FFA levels in both hyperthyroid and control subjects; the lowest FFA levels of hyperthyroid subjects induced by acipimox were similar to those of control subjects. After acipimox pretreatment, GH responses to GHRH increased significantly (P < .05); the mean peak plasma GH level (25.9 +/- 4.6 micrograms/L) was similar to the peak GH levels of control subjects during the GHRH test, and the area under the GH response curve (41.1 +/- 6.7 micrograms/L x 2 h) was even higher than that of control subjects with the GHRH test.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1995

Multiple intracellular Ca2+ pools exist in human foreskin fibroblast cells: the effect of BK on release and filling of the non-cytosolic Ca2+ pools.

Previously, we have used the classical approach to examine intracellular calcium stores in human foreskin fibroblasts (HSWP) cells. In this classical protocol cells are first permeabilized and then allowed to fill their Ca2+ reservoirs with 45Ca2+ in the presence of ATP. In this paper we present an alternative method to examine intracellular calcium pools. In this alternate protocol, whole cells are loaded to isotopic steady-state with 45Ca2+ and then permeabilized using digitonin. Comparison of the Ca2+ content of cells treated with these two methodologies reveals that cells treated with the alternate protocol have a Ca2+ content 3 orders of magnitude higher than those treated with the classical protocol. Using this alternative technique we demonstrate that there are 3 intracellular calcium pools in HSWP cells. These pools are: (i) an IP3-sensitive, thapsigargin-sensitive Ca2+ pool; (ii) an IP3-insensitive, thapsigargin-sensitive Ca2+ pool; and (iii) an ionomycin sensitive Ca2+ pool. The relationship between the Ca2+ pool mobilized by BK treatment and by IP3 treatment is also explored. Microinjection data shown here suggest that IP3 can mobilize all of the intracellular Ca2+ mobilized by BK. However, in the permeabilized system BK pretreatment followed by IP3 treatment can release more Ca2+ than can be release by IP3 treatment alone. We suggest one plausible explanation for this observation: when cells are treated using the alternative permeabilization protocol, communication occurs between an IP3-sensitive and an IP3-insensitive calcium pool. Thus BK pretreatment would empty the IP3-sensitive Ca2+ pool. This pool would subsequently be refilled with Ca2+ from a previously untapped, IP3-insensitive, Ca2+ reservoir and more Ca2+ would be available for subsequent release by IP3 treatment.

Calcium↗
PubMed1995

"Strict" blood pressure control and progression of renal disease in hypertensive nephrosclerosis.

Hypertensive nephrosclerosis is a progressive renal disease and the leading cause of end-stage renal disease (ESRD) in blacks in the United States. It is generally believed that hypertensive renal injury is responsible for progressive renal failure; however, it is not known whether pharmacologic lowering of blood pressure to any level prevents progression of renal disease. Accordingly, we performed a long-term prospective randomized trial to determine whether "strict" [diastolic blood pressure (DBP) 65 to 80 mm Hg] versus "conventional" (DBP 85 to 95 mm Hg) blood pressure control is associated with a slower rate of decline in glomerular filtration rate. Eighty-seven non-diabetic patients (age 25 to 73; 68 black, 58 male) with long-standing hypertension (DBP > or = 95 mm Hg), chronic renal insufficiency (GFR < or = 70 m/min/1.73 m2) and a normal urine sediment were studied. DBP was pharmacologically lowered to < or = 80 mm Hg (3 of 4 consecutive measurements at 1 to 4 weeks intervals) after which patients were randomized. DBP and GFR (renal clearance of 125I-iothalamate) were measured at baseline, at three months and every six months post-randomization. The rate of decline in GFR (GFR slope, in ml/min/1.73 m2/year), estimated by the method of maximum likelihood in a mixed effects model, was the primary outcome variable. In a secondary analysis, 50% reduction in GFR (or a doubling of serum creatinine) from baseline, ESRD and death were combined.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

MELAS syndrome associated with diabetes mellitus and hyperthyroidism: a case report from Taiwan.

MELAS syndrome is a form of mitochondrial myopathy with manifestations of seizure, stroke-like syndrome, lactic acidosis, ragged red muscle fibres and mitochondrial encephalopathy. The syndrome has been reported in association with a variety of endocrine and metabolic disorders including diabetes mellitus (DM), hypothalamo-pituitary hypofunction, hypothalamic growth hormone deficiency and delayed puberty. Mitochondrial DNA (mtDNA) point mutation may be the major pathological defect. However, association of MELAS syndrome with hyperthyroidism has not previously been reported. A case is reported from Taiwan of a 32-year-old woman suffering from MELAS syndrome with associated DM and hyperthyroidism. When the latter was diagnosed in April 1988, the patient underwent subtotal thyroidectomy. There was no family history of thyroid disease. Because of repeated seizures, she had computed tomography (CT) and magnetic resonance imaging (MRI) of the brain which showed focal, low-density lesions over the cerebral hemispheres. Both serum and cerebral spinal fluid lactic acid levels were elevated. Mild elevations of serum T4 and T3 and a high titre of TSH receptor antibody were still present. Hyperglycaemia was noted during hospitalization and DM confirmed by oral glucose tolerance test. Muscle biopsy showed ragged red fibres. DNA analysis showed an A-to-G transition at the 3243rd nucleotide position of the tRNA(Leu(UUR)) gene of the mtDNA from the patient. Quantitative polymerase chain reaction (PCR) and restriction analysis revealed that about 60% of the blood mtDNA was of mutant type. The patient received antithyroid drugs for hyperthyroidism, diet control for DM and anti-epileptic drugs for seizure.

Adult↗
PubMed1995

CPEO and carnitine deficiency overlapping in MELAS syndrome.

Mitochondrial myopathy, encephalopathy with lactic acidosis and stroke-like episodes (MELAS) syndrome is one of the mitochondrial encephalomyopathies that has distinct clinical features including stroke-like episodes with migraine-like headache, nausea, vomiting, encephalopathy and lactic acidosis. We report a 27-year-old woman who presented with partial seizure, stroke-like episodes including hemiparesis, hemianopia and hemihypethesia, sensorineural hearing loss, migraine-like headache, and lactic acidosis. Brain computed tomographic scan showed encephalomalacia in the right parieto-occipital area and recent hypodensity in the left temporoparieto-occipital area with cortical atrophy. Muscle biopsy revealed ragged-red fibers and paracrystaline inclusions in the mitochondria. Genetic study revealed an A to G point mutation at nucleotide position (np) 3243 of mitochondrial DNA. External ophthalmoplegia and ptosis were also found during two exaggerated episodes in this patient. Therefore, the overlapping syndrome of chronic progressive external ophthalmoplegia in the MELAS syndrome is considered in this case. Furthermore, we also found carnitine deficiency in this patient and she was responsive well to steroid therapy. Muscle biopsy also revealed excessive lipid droplets deposits. Therefore, the carnitine deficiency may occur in MELAS syndrome with the A to G point mutation at np 3243. We recommend the steroid or carnitine supplement therapy be applied to the MELAS syndrome with carnitine deficiency.

Adult↗
PubMed1995

Neonatal-onset chronic intestinal pseudo-obstruction syndrome.

Between January 1985 and January 1990, six cases of neonatal-onset chronic intestinal pseudo-obstruction syndrome (CIPS) were identified. Failure to gain weight in six cases, abdominal distention in five, and vomiting in five were the most common presenting symptoms. The contrast studies of the gastrointestinal tract demonstrated delayed transit time in 6/6, jejunal or ileal dilatation in 1/6, megaduodenum in 1/6, dilatation of the colon with barium retention in 4/6, and microcolon in 1/6. Urinary tract involvement was noted in three patients. Laparotomy, performed in three patients, revealed no mechanical obstruction. Except for hypoganglionosis in Patient 4, no recognizable neuropathy or myopathy was noted histopathologically. Four patients expired within 2 months after discharge. We conclude that CIPS with neonatal onset should be suspected when infants have urinary retention and abdominal distention or constipation beginning at birth or soon after. The prognosis of CIPS presenting in the newborn period appears worse than that presenting in childhood or adulthood.

Abdomen↗
PubMed1995

Acipimox potentiates growth hormone (GH) response to GH-releasing hormone with or without pyridostigmine by lowering serum free fatty acid in normal and obese subjects.

Obesity is associated with an impairment of normal GH secretion and blunted responses to all stimuli. Recent reports suggest that increased somatostatinergic activity is the basis for the GH derangement of obesity. However, the basic mechanism of this alteration is still being debated. The high plasma free fatty acid (FFA) is frequently observed in obesity. FFA participates in the regulation of pituitary GH secretion. To determine whether the derangement of GH secretion in obesity is associated with high plasma FFA levels, several tests with GHRH with or without pyridostigmine (PYR) and acipimox (ACX), antilipolytic agents able to decrease FFA, were undertaken in six obese and seven normal control subjects. In obese subjects, the GH response (mean peak +/- SEM: 8.9 +/- 1.1 ug/L) to GHRH-(1-29) (1 ug/kg, i.v.) was significantly blunted when compared with the response in normal control subjects (25.7 +/- 1.8 ug/L; P < 0.05). After PYR (120 mg), the response to GHRH was enhanced in the obese subjects (21.4 +/- 4.9 ug/L; P < 0.05) and was similar to that of the controls with GHRH only, but remained significantly reduced compared with controls treated with PYR plus GHRH (43.2 +/- 6.0 ug/L; P < 0.05). Basal FFA levels were higher than those of normal controls (P < 0.05). ACX (500 mg) decreased FFA levels in both obese and normal subjects; the lowest FFA levels of obese subjects at 15 min were similar to those of normal controls. ACX also potentiated GHRH-stimulated GH response in both obese and normal subjects. The GH responses potentiated by ACX in obesity (22.7 +/- 5.5 ug/L) were similar to those of PYR plus GHRH in obese subjects and GHRH in normal controls, but they were lower than those of control treated with ACX plus GHRH (50.8 +/- 6.7 ug/L; P < 0.05). After the combined pretreatment with ACX and PYR, GH responses in obesity (44.1 +/- 6.0 ug/L) were significantly higher than those in GHRH test, PYR plus GHRH, and ACX plus GHRH in obese subjects (P < 0.05), and they were similar to PYR plus GHRH or ACX plus GHRH in normal controls. However their enhanced GH responses were reduced compared with the control with ACX plus PYR plus GHRH (64.9 +/- 4.5 ug/L; P < 0.05). Our results are in agreement with the hypothalamic hypothesis: an increase in somatostatinergic tone is responsible for the blunted GH response to GHRH in obesity.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1995

Relationships among 64k autoantibodies, pancreatic beta-cell function, HLA-DR antigens and HLA-DQ genes in patients with insulin-dependent diabetes mellitus in Korea.

OBJECTIVES: Among autoantibodies detected in patients with insulin-dependent diabetes mellitus (IDDM), antibodies to 64,000(Mr) islet protein(64k), now recognized as glutamic acid decarboxylase(GAD), appear to be an even more predictive marker of IDDM than islet cytoplasmic antibody (ICA) or insulin autoantibody (IAA). We examined the relationships among 64k autoantibodies, pancreatic beta-cell function, HLA-DR antigens and HLA-DQ genes in patients with IDDM in Korea. METHODS: To identify the 64k autoantibody, the immunoprecipitation method was performed for 35 patients with IDDM and 10 normal controls. In patients with IDDM, serum C-peptide levels were measured and HLA-DR typings and HLA-DQA1 and DQB1 gene typings were performed. RESULTS: 12 of 35 (34%) patients with IDDM were positive for 64k autoantibody in contrast to none of 10(0%) normal controls. There were no differences in residual pancreatic beta-cell function between 64k autoantibody positive and negative groups. 64k autoantibody was detected more frequently in patients with recent (duration < 6 months, 10/25[40%]) and young -aged(aged < 15 years, 7/18[39%]) onset of IDDM. All of 3(100%) patients with HLA-DR3/DR4 heterotypes were positive in 64k autoantibody, in contrast to 1 of 7(14%) patients without HLA-DR3 nor DR4. The frequencies of HLA-DQA1*0301, HLA-DQB1*0201, DQB1* 0302 and DQB1*0303 gene types were higher in patients with 64k autoantibody (12/12 [100%]) vs. without 64k autoantibody 18/22[81%], 5/11[45%] vs. without 64k autoantibody 5/22[23%], 5/11[45%] vs. without 64k autoantibody 8/22[36%] and 6/11 [55%] vs. without 64k autoantibody 9/22[41%]. CONCLUSIONS: There results suggest that 64k autoantibodies have some relationship with HLA-DR, DQA1 and DQB1 genes, but not with residual pancreatic beta-cell function in Korean patients with IDDM.

Adolescent↗
PubMed1994

Surgery for seizure-related structural lesions of the brain with intraoperative acute recording(ECoG) and functional mapping.

Epilepsy surgery has been demonstrated to be an effective alternative treatment for intractable partial or localization related epilepsy. Primary intracranial neoplasms and other structural lesions of the brain are important etiological factors in patients with partial seizure disorders. A neuroimaging identified lesion in patients with seizures, not necessarily medically refractory, may also be an indication for surgery in selected patients. Twelve patients operated on under local or general anesthesia for resection surgery underwent intraoperative recording(electrocorticogram) and/or functional mapping by electrical stimulation or somatosensory evoked potentials-(SSEPs) for identification of the secondary epileptogenic area and/or functional area; 2 meningiomas, 5 astrocytomas, 1 gangliocytoma, 1 abscess, 1 small AVM, 1 cysticercosis and one gliosis by previous intracerebral hemorrhage with middle cerebral artery(MCA) aneurysm. Among these, additional corticectomy or anterior temporal lobectomy was performed in eleven patients. All the patients did well after surgery with good outcomes as seizure free in nine(75%) out of 12 patients with 11.9 months of follow-up period, without any neurological deficits. Intraoperative recording and functional mapping of adjacent areas of the structural lesions of the brain are useful in surgery and can guide the extent of further resection.

Adolescent↗
PubMed1994

Duplex ultrasonographic assessment of gut blood flow velocity: effect of meal composition in normal full-term newborns after first feed.

We used transcutaneous duplex Doppler ultrasound to measure superior mesenteric artery and celiac artery blood flow velocity in 45 normal healthy newborn infants. Doppler indices of PSV, TAMV, EDV, and PI were measured immediately before and after feeding at 15 minute intervals up to 75 minutes. Maximal changes were compared with preprandial baseline values. There were no significant differences between the preprandial and postprandial blood pressures and heart rates. In the superior mesenteric artery the PSV, TAMV, and EDV rose progressively and peaked 30 minutes after feeding in both the milk-fed group and the 5% glucose, water-fed group over baseline (73 versus 41% and 110 versus 63%, 130 versus 100%) (P < 0.05). The PI decreased significantly in the milk-fed group only. There were no significant changes in any blood flow velocity parameters derived from the celiac artery. We conclude that duplex ultrasonography provides a noninvasive means of studying the reactivity of the splanchnic arterial circulation to different stimuli. The chemical composition of the meal is a significant factor determining postprandial mesenteric hyperemia.

Blood Flow Velocity↗
PubMed1994

Reliability, validity and structure of the Chinese Geriatric Depression Scale in a Hong Kong context: a preliminary report.

Depression is one of the commonest psychiatric illness in the elderly. Screening instruments of depression can greatly facilitate its identification in the community, leading to early recognition and diagnosis. The Geriatric Depression Scale was translated into Chinese and its reliability, validity and factor structure examined in a population of Chinese elderly in Hong Kong. One hundred and thirteen normal and 80 depressed elderly subjects were studied and a cut-off score of 15 on the scale was found to be optimal. The scale's reliability and validity was satisfactory and thus it is a promising instrument for screening geriatric depression in Hong Kong.

Aged↗
PubMed1992

Hydrogen bonding to the bound dioxygen in oxy cobaltous myoglobin reduces the superhyperfine coupling to the proximal histidine.

Electron spin echo envelope modulation (ESEEM) spectroscopy was used to study the electron-nuclear coupling in two oxygenated cobalt-substituted hemoproteins, myoglobin (oxyCoMb) and a monomeric hemoglobin from Glycera dibranchiata (oxyCoHbgly). The modulation frequency components in ESEEM spectra of both proteins arose from the coupling to the N epsilon of the proximal histidyl imidazole. The hyperfine and quadrupole coupling parameters for these two nitrogens, calculated by computer spectral simulation, are Aiso = 2.46 MHz, e2qQ = 2.15 MHz, and eta = 0.4 for oxyCoMb and Aiso = 3.70 MHz, e2qQ = 2.70 MHz, and eta = 0.5 for oxyCoHbgly. A hyperfine coupling of 0.6 MHz, found for oxyCoMb in D2O but not for oxyCoHbgly in D2O, was assigned to the coupling to a deuteron that is hydrogen-bonded to the O2 ligand in oxyCoMb. This hydrogen bonding is believed to be responsible for the reduction in hyperfine and nuclear quadrupole coupling to the proximal histidyl imidazole N epsilon in oxyCoMb. A molecular orbital model for O2 adducts of cobaltous compounds [Tovrog et al. (1976) J. Am. Chem. Soc. 98, 5144] was used to understand the hydrogen bond-induced reduction in 14N superhyperfine coupling in oxyCoMb.

Animals↗