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Biomedical subjects

M J McDonald

Publications and source records attributed to M J McDonald.

16 recordsLinked to original sources
PubMed1992

Hb Rancho Mirage [beta 143(H21)His----Asp]; a variant in the 2,3-DPG binding site showing normal oxygen affinity at physiological pH.

Hb Rancho Mirage was detected in a 17-year-old male in association with a mild anemia. Hemoglobin electrophoresis revealed the variant had a mobility between Hbs A and J on cellulose acetate (pH 8.6) and a mobility like Hb F on citrate agar (pH 6.4). A substitution of His----Asp was found at position 143 in the beta chain, a residue that contributes to the anionic 2,3-DPG binding site in Hb. This variant exhibited normal oxygen affinity at physiologic pH and reduced affinity at alkaline pH. This suggested a subtle shift in the allosteric equilibrium due most likely to the introduction of a negative charge that stabilized the 2,3-DPG pocket. Both homotrophic (heme-heme) and heterotropic (2,3-DPG and protons) effects were reduced; this might be a consequence of an alteration in the carboxyl terminal region of the beta-subunits. Although a His----Asp substitution would be considered to cause reasonable disruption of the 2,3-DPG and C-terminal conformation of the beta- subunits, the properties of Hb Rancho Mirage suggest that, in fact, there appear to be no major perturbation of the critical C-terminal residues.

2,3-Diphosphoglycerate↗
PubMed1991

Safety and efficacy of a new regimen of intravenous recombinant tissue-type plasminogen activator potentially suitable for either prehospital or in-hospital administration.

The safety and efficacy of a new regimen of intravenous recombinant tissue-type plasminogen activator (rt-PA) potentially suitable for either pre- or in-hospital administration were assessed in 60 patients with acute myocardial infarction in an open label coronary angiographic study. The regimen consisted of a 20-mg bolus dose followed 30 min later by a delayed infusion of 80 mg over 2 h. This regimen was designed to facilitate prehospital administration of rt-PA. Infarct-related artery patency (Thrombolysis in Myocardial Infarction [TIMI] grade 2 or 3 flow) was observed in 40 of 53 patients at 60 min (75.5%, 95% confidence intervals [CI] 61% to 84%) and in 55 of 60 patients at 90 min (91.7%, 95% CI 80% to 95%) after the rt-PA bolus. By 90 min the majority of patients (55%) exhibited TIMI grade 3 flow; infarct artery patency at 120 min was 84.9%. During hospitalization definite recurrent ischemia occurred in nine patients (15%); nonfatal recurrent infarction was noted in one (1.7%). Four patients (6.7%) experienced major bleeding, including one with intracranial bleeding. There were seven deaths (11.7%). Mortality was significantly influenced by the occurrence of cardiogenic shock, which was present in five patients at the time of enrollment. Blood fibrinogen levels were obtained before and during rt-PA infusion. At baseline and 30 and 150 min after the bolus dose, the mean fibrinogen level (+/- SD) was 284.83 +/- 77.39, 237.96 +/- 76.92 and 192.04 +/- 57.82 mg/dl, respectively. Compared with the baseline value, there was a significant (p less than 0.05) decrease in fibrinogen at both 30 and 150 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Structural, functional, and subunit assembly properties of hemoglobin Attleboro [alpha 138 (H21) Ser----Pro], a variant possessing a site maturation at a critical C-terminal residue.

Hemoglobin Attleboro, a new alpha-chain variant with a substitution of proline for serine at position 138 (H21), was found to be a noncooperative high-affinity hemoglobin (P50 = 0.26 mmHg at pH 7 and 20 degrees C) which lacked an alkaline Bohr effect. Addition of 2,3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP) led to a decrease in oxygen affinity but to no alteration in either Bohr effect or cooperativity. Ligand binding kinetics studies revealed an overall rate of oxygen dissociation at pH 7.0 and 20 degrees C that was 2.7-fold slower than that for Hb A. At pH 8.5, the kinetic profile was identical with that at pH 7, confirming the absence of a Bohr effect for this variant hemoglobin. Measurement of the rate of oxygen dissociation with carbon monoxide replacement indicated a lack of cooperativity. Sedimentation velocity experiments yielded s20,w values of 2.8 and 4.3 for 65 microM solutions of oxyhemoglobins Attleboro and A, respectively (indicating an enhancement in the oxy dimer population of this variant). Studies of the carbon monoxide combination of this variant revealed an association rate 20-fold faster than that for Hb A; only in the presence of a 1000-fold molar excess of IHP was there a significant reduction in the overall rate. Rapid-scan and traditional stopped-flow experiments conducted in the Soret Soret region demonstrated an alteration in the structure and rate of assembly of the deoxy tetramer of Hb Attleboro relative to that of Hb A. The abnormal properties of this hemoglobin variant can be attributed to major perturbations in the C-terminal region.

Amino Acid Sequence↗
PubMed1979

Nonenzymatic glycosylation of human hemoglobin at multiple sites.

The most abundant minor hemoglobin component of human hemolysate is Hb A1c, which has glucose bound to the N-terminus of the beta chain by a ketoamine linkage. Hb A1c is formed slowly and continuously throughout the 120 day lifespan of the red cell. It can be synthesized in vitro by incubating purified hemoglobin with 14C-glucose. Other minor components, Hb A1a1 and Hb A1a2 are adducts of sugar phosphates at the N-terminus of the beta chain. Hb A1b contains an unidentified nonphosphorylated sugar at the beta N-terminus. In addition, a significant portion of the major hemoglobin component (Hb Ao) is also glycosylated by a glucose ketoamine linkage at other sites on the molecule, including the N-terminus of the alpha chain and the epsilon-amino group of several lysine residues on both the alpha and the beta chains. The results indicate that the interaction of glucose and hemoglobin is rather nonspecific and suggests that other proteins are modified in a similar fashion.

Blood Glucose↗
PubMed1978

Acute selenium poisoning: case report.

A case of self-poisoning with sodium selenate sheep drench, along with blood and urine levels of selenium, is reported. Treatment included gastric lavage, diuresis, vitamin C, and dimercaprol, and the patient recovered without sequelae.

Acute Disease↗
PubMed1978

Glycosylated minor components of human adult hemoglobin. Purification, identification, and partial structural analysis.

Human hemolysate contains several minor components designated Hb A1a, Hb A1b, Hb A1c, which are post-translational modifications of the major hemoglobin component A0. Individuals with diabetes mellitus have elevated levels of Hb A1c, a hemoglobin modified with a glucose moiety at the NH2 terminus of each beta chain. A new chromatographic technique using Bio-Rex 70 is described which not only allows complete separation of Hb A1a from Hb A1b but also resolution of Hb A1a into two components, designated Hb A1a1 and Hb A1a2. Carbohydrate determinations with the thiobarbituric acid procedure revealed that Hb A1a1, Hb A1a2, and Hb A1b as well as Hb A1c were glycosylated. Total phosphate analysis revealed 2.06 and 1.01 mol of phosphorus/alphabeta dimer for Hb A1a1 and Hb A1a2 respectively; Hb A1b and Hb A1c contained no detectable phosphate. Hemoglobin incubated with D-[14C]glucose-6-P co-chromatographs precisely with Hb A1a2, strongly suggesting that Hb A1a2 is glucose-6-P hemoglobin. Levels of Hb A1a1 and Hb A1a2 are normal in individuals with diabetes mellitus. Furthermore, diabetic red cells contain normal levels of glucose-6-P. Therefore, glucose-6-P hemoglobin does not serve as a significant precursor to Hb A1c. Instead Hb A1c is formed by the direct reaction of hemoglobin with glucose. This suggests that hemoglobin can serve as a model system for nonenzymatic glycosylation of protein.

Adult↗
PubMed1977

Ligand-induced conformational changes in spin label-modified human hemoglobins and chains and their carboxypeptidase A-digested derivatives.

The reactive sulfhydryls of human adult and fetal hemoglobin and the single sulfhydryl of isolated gamma chains have been spin labeled with N-(1-oxyl-2,2,5,5-tetramethyl-3-pyrrolidinyl) iodoacetamide. Similar electron paramagnetic spectral differences between oxy- and deoxy-modified hemoglobins were observed for both these hemoglobins and for the isolated chains, indicating that ligand-induced conformational changes occur in isolated hemoglobin subunits as well as intact hemoglobin tetramers. Ligand induced changes in the reactivity of p-hydroxymercuribenzoate with the sulfhydryl groups of both intact hemoglobins and isolated subunits, observed by McDonald and Noble (1974) J. Biol. Chem. 249, 3161-3165), led them to draw a similar conclusion. Following carboxypeptidase A digestion of these modified hemoglobins and gamma chains, a procedure which specifically removes the two C-terminal residues of the beta or gamma chains, spectral differences between the liganded and unliganded spin-labeled derivatives still persisted. However, the magnitude of this difference was not only more reduced in the case of the hemoglobins than in that of the subunits but the spectra of both the oxy and deoxy derivatives of the hemoglobins were characteristic of the oxy derivative of a cooperative tetrameric hemoglobin. These findings support the premise that the COOH-terminal end of the beta or gamma chain contributes, although possibly to different extents, to the spectral differences exhibited by both the spin-labeled hemoglobins and chains.

Carboxypeptidases↗
PubMed1975

Rat haemoglobin heterogeneity. Two structurally distinct alpha chains and functional behaviour of selected components.

Six haemoglobins were separated analytically from haemolysates of adult Wistar rats (Rattus norvegicus) by cellulose acetate electrophoresis and preparatively by DEAE-cellulose chromatography. The globin chains were separated from unfractionated haemolysates by CM-cellulose chromatography by using a non-linear formic acid-pyridine gradient followed by CM-cellulose chromatography in 8M-urea by using a gradient of increasing Na+ concentration in phosphate buffer, pH 6.7. Two alpha chains and three non-alpha chains were identified. Chains isolated from purified haemoglobins were correlated with chains isolated from unfractionated haemolysates by electrophoresis on urea-starch gels to make presumptive assignments of the subunit composition of the six haemoglobin tetramers. Partial amino acid sequences were determined for the major and minor alpha chains. The oxygen equilibria of two of the major haemoglobin components and of the unfractionated haemolysate were examined at pH 7.5 and 8.0. The two purified haemoglobins exhibited similar oxygen affinities; the haemolysate, however, had a lower oxygen affinity than either of the two purified haemoglobins. Both the haemolysate and the two haemoglobins showed an alkaline Bohr effect larger than that of human haemoglobin A.

Amino Acid Sequence↗
PubMed1975

Magnitude of subunit inequivalence for oxygen release from hemoglobin: reinvestigation of the oxygen-pulse experiment.

Two hypotheses have been presented to explain the grossly biphasic oxygen release kinetics observed when hemoglobins are studied with the oxygen pulse technique [Gibson (1973) Proc. Nat. Acad. Sci. USA 70, 1-4]. Hypothesis I suggests that the two phases result from cooperativity, with the fast phase being oxygen release from the low affinity (T) state and the slow phase being oxygen release from molecules that have switched to the high affinity (R) state. Hypothesis II suggests that the biphasic curves are due to a large (factor of 20-30) difference in oxygen release from the two types of subunits within deoxyhemoglobin. In order to experimentally discriminate between these two hypotheses, we reinvestigated the oxygen pulse reaction for hemoglobin Kansas (alpha2 beta2 102 Asn leads to Thr) in the absence and presence of inositol hexaphosphate, since recent high resolution nuclear magnetic resonance studies have shown that this allosteric cofactor stabilizes hemoglobin Kansas in T even when fully liganded [Ogawa, Mayer, and Shulman (1972) Biochem. Biophys. Res. Commun. 49, 1485-1491]. The results of these studies clearly favor hypothesis I over hypothesis II as being the correct interpretation for the oxygen pulse results. However, we have found evidence that suggests that oxygen release and binding in T are surprisingly faster than previously observed. Furthermore, within T, there is some spectral and kinetic heterogeneity for oxygen release from adult hemoglobin and hemoglobin Kansas. The magnitude of this kinetic heterogeneity in T appears to be about the same as that seen in the high affinity, R, state. The exchange of hypothesis II for hypothesis I more strongly favors views of cooperative oxygen binding involving both types of subunits, as required if the allosteric model of Monod, Wyman, and Changeux [(1965) J. Mol. Biol. 12, 88-118] is considered operative.

Adult↗