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S M Miller

Publications and source records attributed to S M Miller.

At least 163 records · Page 9Linked to original sources
PubMed1983

Magnitude of intrinsic isotope effects in the dopamine beta-monooxygenase reaction.

Intrinsic primary hydrogen isotope effects (kH/kD) have been obtained for the carbon-hydrogen bond cleavage step catalyzed by dopamine beta-monooxygenase. Irreversibility of this step is inferred from the failure to observe back-exchange of tritium from TOH into substrate under conditions of dopamine turnover; this result cannot be due to solvent inaccessibility at the enzyme active site, since we will demonstrate [Ahn, N., & Klinman, J. P. (1983) Biochemistry (following paper in this issue)] that a solvent-derived proton or triton must be at the enzyme active site prior to substrate activation. As shown by Northrop [Northrop, D. B. (1975) Biochemistry 14, 2644], for enzymatic reactions in which the carbon-hydrogen bond cleavage step is irreversible, comparison of D(V/K) to T(V/K) allows an explicit solution for kH/kD. Employing a double-label tracer method, we have been able to measure deuterium isotope effects on Vmax/Km with high precision, D(V/K) = 2.756 +/- 0.054 at pH 6.0. The magnitude of the tritium isotope effect under comparable experimental conditions is T(V/K) = 6.079 +/- 0.220, yielding kH/kD = 9.4 +/- 1.3. This result was obtained in the presence of saturating concentrations of the anion activator fumarate. Elimination of fumarate from the reaction mixture leads to high observed values for isotope effects on Vmax/Km, together with an essentially invariant value for kH/kD = 10.9 +/- 1.9. Thus, the large disparity between isotope effects, plus or minus fumarate, cannot be accounted for by a change in kH/kD, and we conclude a role for fumarate in the modulation of the partitioning of enzyme-substrate complex between catalysis and substrate dissociation. On the basis of literature correlations of primary hydrogen isotope effects and the thermodynamic properties of hydrogen transfer reactions, the very large magnitude of kH/kD = 9.4-10.9 for dopamine beta-monooxygenase suggests an equilibrium constant not very far from unity for the carbon-hydrogen bond cleavage step. This feature, together with the failure to observe re-formation of dopamine from enzyme-bound intermediate or product and overall rate limitation of enzyme turnover by product release, leads us to propose a stepwise mechanism for norepinephrine formation from dopamine in which carbon-hydrogen bond cleavage is uncoupled from the oxygen insertion step.

Animals↗
PubMed1983

Interacting effects of information and coping style in adapting to gynecologic stress: should the doctor tell all?

This study explored the interacting effects of personal dispositions and situational conditions on the stress response. Forty gynecologic patients about to undergo a diagnostic procedure (colposcopy) were divided into information seekers (monitors) and information avoiders (blunters). Half in each group were exposed to voluminous preparatory information, and half to the usual low level of information. Subjective, physiological, and behavioral measures of arousal and discomfort were obtained before, during, and after the procedure. Overall, low-information patients expressed less subjective arousal than high-information patients, and blunters showed less subjective and behavioral arousal than monitors. In addition, patients' level of psychophysiological arousal was lower when the level of preparatory information was consistent with their coping style; that is, blunters were less aroused with low information and monitors were less aroused with high information. Further evidence was gained for the utility and validity of a new scale for identifying monitors and blunters.

Adaptation, Psychological↗
PubMed1983

Biochemical and structural characterization of membrane fractions from bovine lens.

Plasma membranes of vertebrate lens fiber cells contain large numbers of gap junctions that may provide pathways for metabolic cooperation. Characterization of fiber cell gap junctions is thus necessary to understand this function. In this study, plasma membrane fractions were isolated from bovine lens according to established techniques, but without urea, detergents, or proteolytic enzymes. Electron microscopy indicated that isolated plasma membranes with gap junctions form double-membrane vesicles, and gap junctions comprised approximately 35% of the total membrane area in the crude fraction. These vesicles were impermeable to cationized ferritin, suggesting that they were sealed, and may be useful for permeability studies. Treatment of the crude fraction with 2.5% beta-mercaptoethanol or dithiothreitol caused reversible separation of junctional membranes, suggesting that disulfide bonds may be important in maintaining gap junction structure. Fractions with varying proportions of gap junctions were isolated using linear sucrose density gradient centrifugation. The proportional area of gap junction membrane versus total membrane in the various fractions ranged from 10% to at least 51%. The following plasma membrane enzymes were assayed in all fractions: Mg++-ATPase, Ca++-ATPase, alkaline phosphatase, phosphodiesterase, 5'-nucleotidase, and Na+, K+-ATPase. There was no correlation between enzyme activity and gap junction enrichment. This suggests that these enzymes are not associated with fiber cell gap junctions.

5'-Nucleotidase↗
PubMed1983

New perspectives on vitamin D.

Our perception of vitamin D has evolved since the early part of this century. As an active, dihydroxylated metabolite vitamin D is acknowledged today not as an essential dietary factor but rather as a major calciotropic hormone. This paper summarizes current understanding of the formation and action of vitamin D in health and disease. The importance of laboratory assessment of serum vitamin D metabolites in the diagnosis and management of disorders of calcium and phosphorus metabolism is discussed.

Adult↗
PubMed1978

Cocaine toxicity.

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Anesthetics, Local↗