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H E Harris

Publications and source records attributed to H E Harris.

52 records · Page 3Linked to original sources
PubMed1976

Myosin-paramyosin cofilaments: enzymatic interactions with F-actin.

The interaction between paramyosin and myosin has been studied by enzymological methods. Clam adductor paramyosin inhibits the actin-activated, Mg2+-requiring ATPase of both clam adductor and rabbit skeletal muscle myosins. Myosin and paramyosin must be rapidly coprecipitated for this inhibition. Incubation with F-actin in the absence of ATP does not alter this effect. This inhibition follows a hyperbolic function with respect to paramyosin concentration. Slow precipitation by dialysis of myosin and paramyosin together leads to copolymers with actin-activated ATPase equivalent to that of slowly formed myosin filaments. Both kinds of slowly formed filaments have enzymatic properties distinct from those of the rapidly precipitated proteins. Paramyosin is competitive with F-actin for their effects upon myosin. The apparent affinity of myosin for F-actin is markedly reduced by association with paramyosin, but the extrapolated maximal velocity of actomyosin is unaffected. The specificity of this inhibition is strongly suggested by marked quantitative differences between native and cleaved paramyosins. No inhibition of intrinsic myosin ATPase by paramyosin is seen. These studies suggest that at least two types of condition-dependent association between myosin and paramyosin are possible. One class of interactions is associated with enzymic inhibition in rapidly coprecipitated filaments, whereas slowly formed cofilaments exhibit catalytic activity similar to that of identically treat-d myosin and have a characteristic 14.5 nm axial repeat.

Actins↗
PubMed1975

Conformational properties of pig-heart cytoplasmic aspartate aminotransferase. Circular-dichroism and absorption-spectroscopic study of dicarboxylate binding.

1. The interaction between aspartate aminotransferase and dicarboxylates of various chain lengths and geometries has been studied from pH 6.5 TO 8.5 by circular dichroism (CD) and absorption spectroscopy. Liganding causes protonation of the pyridoxal phosphate-enzyme Schiff's base complex; the consequent changes in optical properties deltaAlambda, deltaCDlambda at the coenzyme maxima (lambda = 363 or 430 nm) are analysed for binding constants and the degree of perturbation of the coenzyme protonic dissociation constant, pKa. 2. Aliphate dicarboxylates follow linear binding functions for all optical parameters; in contrast, m and p-phthalates follow non-linear binding functions for both deltaAlambda and deltaCDlambda, implying that successive phthalate ligands bind with decreasing affinity. The ratio detlaCDlambda is effectively constant for a given ligand and the characteristic values for aromatic ligands indicate a changed environment for the coenzyme. 3. Inspection of the non-linear process for phthalates suggests that initially, binding occurs with high affinity, but with characteristically small effects on pKa. It is inferred that alipathic and aromatic dicarboxylates bind at different subsites in the active site region, perturbing the coenzyme pKa by an indirect protein-mediated mechanism. 4. Non-linearity of binding could derive from multiple binding to an individual subunit. Alternatively, different single sites may exist on adjacent subunits of the dimer, implying non-equivalence between otherwise identical subunits, expressed in properties involving groups close to the active site.

Animals↗
PubMed1975

Interaction of myosin and paramyosin.

The interaction of myosin and paramyosin was investigated by enzymological and ultrastructural techniques. The actin-activated Mg+2 ATPase of rabbit skeletal muscle myosin can be inhibited by clam adductor paramyosin. Both proteins must be rapidly coprecipitated to form filaments for this inhibition. Slowly formed cofilaments are fully activatable by F-actin. In both cases, the cofilaments possess unique structural characteristics when compared to homofilaments. The mode of inhibition appears to be competitive when different concentrations of paramyosin and F-actin are compared. The apparent affinity of the myosin heads for actin is reduced by the presence of paramyosin within rapidly reconstituted thick filaments. These results suggest that paramyosin may serve as part of a relaxing mechanism within invertebrate muscles. It is unlikely that paramyosin plays a role in the initiation and maintenance of catch within specialized molluscan muscles.

Actins↗
PubMed1975

The binding of 8-anilinonaphthalene-1-sulphonate to cytoplasmic aspartate aminotransferase from pig heart.

Anilinonaphthalenesulphonate binds to cytoplasmic aspartate aminotransferase with high affinity (Kd about 10 muM) and with a stoicheiometry of one molecule per dimer. It is not displaced by aliphatic or aromatic dicarboxylate substrate analogues. The enzyme is believed to be a symmetrical dimer with identical subunits; it can evidently function asymmetrically in binding anilinonaphthalenesulphonate.

Anilino Naphthalenesulfonates↗
PubMed1969

Pandora.

Explore the source record for details and available documents.

Adult↗
PubMedDate not supplied

Practical approaches for estimating prepregnant body weight.

Measurements of prepregnant body weight have important research and clinical applications. In practice, however, they are not always recorded; even when they are, this information is not always readily available. For this reason, researchers and clinicians have to rely on retrospective estimates of prepregnant weight, which can be estimated using: 1) maternal self-reports, 2) retrospective extrapolation, or 3) standardized estimates that correct for weight gained during early pregnancy. The aim of the present study was to examine the relative merits of these three approaches. Maternal self-reports tend to be unreliable and biased, being influenced by a variety of sociodemographic characteristics that generally underestimate true prepregnant body weight. Estimates of prepregnant weight based on retrospective extrapolation are vulnerable to measurement error, transient fluctuations in body weight, and incorrectly assume that the rate of weight gain is constant throughout pregnancy. Standardized estimates that correct for weight gained during early pregnancy incorrectly presume that there is little interindividual variation in gestational weight gain and that weight gain is similar for each woman in consecutive pregnancies. Because none of these techniques can provide a precise measure of prepregnant weight, researchers have little alternative but to recruit and weigh women before they become pregnant, although measurements of body weight recorded during the first trimester of pregnancy may provide a reasonable indication of prepregnant weight. For clinicians, self-reports of prepregnant weight or measurements recorded early in pregnancy are probably sufficiently accurate for practical purposes whenever recent, accurate measurements of prepregnant weight are unavailable.

Anthropometry↗
PubMedDate not supplied

Is there an independent association between parity and maternal weight gain?

The independent associations between parity and maternal body mass index (BMI), and between parity and maternal weight gain, were investigated using a combination of cross-sectional and longitudinal analyses based on a retrospective, repeat-pregnancy study that examined the change in maternal body weight from the beginning of one pregnancy to the beginning of the next. A group of 523 multiparous women who had been weighed regularly during pregnancy, and none of whom had fallen pregnant less than 12 months after the birth of their previous child, were examined. Sociodemographic, behavioural, medical, obstetric and perinatal data, together with antenatal measurements of maternal body weight and height, were abstracted from each mother's obstetric notes. Parity was found to be independently associated with maternal BMI (p < 0.001), gestational weight gain (p < 0.001) and interpregnancy weight gain (p = 0.032). Women of different parities were found to be at differential risk of long-term weight gain for two reasons. First, primiparous women are at risk of long-term weight gain because they gain the most weight during pregnancy, and high gestational weight gain is in itself a risk factor for long-term weight gain. Second, women of higher parity (4+) are at risk of long-term weight gain because they gain more weight in association with pregnancy, irrespective of the amount of weight they gain during their pregnancies. For women of parity 3 or less, the association between maternal body weight and parity appears to be the result of cumulative weight gained during successive pregnancies. For women of greater parity, the association between maternal body weight and parity is partly the result of cumulative excess gestational weight gained during successive pregnancies, and partly the result of gaining more weight from the beginning of one pregnancy to the next at later pregnancies.

Adult↗