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Biomedical subjects

J D Allen

Publications and source records attributed to J D Allen.

At least 127 records · Page 7Linked to original sources
PubMed1978

Multimolecular substrate reactions catalyzed by caabohydrases. Aspergillus oryzae alpha-amylase degradation of maltooligosaccharides.

Aspergillus oryzae alpha-amylase degrades maltooligosaccharides by other pathways besides simple glycosidic bond scission. The utilization of the alternate pathways increases with the concentration of substrate implicating a multimolecular substrate mechanism. Reducing-end labeled and uniformly labeled maltooligosaccharides were used to elucidate these alternate degradation mechanisms. Condensation followed by hydrolysis is not a significant pathway. Transglycosylation is concluded to occur, but no single transglycosylation mechanism can account for all of the experimental data for maltotriose degradation. Rather, a combination of transglycosylations must be invoked.

Amylases↗
PubMed1978

Model for carbohydrase action. Aspergillus oryzae alpha-amylase degradation of maltotriose.

Aspergillus oryzae alpha-amylase catalyzes degradation of oligosaccharides by a variety of pathways. We present here a quantitative study of the degradation of maltotriose by this amylase. Our results lead to a scheme involving multiple transglycosylation reactions and shifted binding due to simultaneous binding of two substrate molecules. The scheme is able to account for the diverse body of information collected for the enzyme. The effect of substrate concentration on the products of maltotriose degradation is correctly predicted over a 10(4)-fold concentration range, and the time course of maltotriose degradation is closely approximated by this scheme. The initial velocity data, which show deviation from Michaelis-Menton kinetics, are also consistent with the formulated scheme. The scheme is proposed as a general model of carbohydrase action.

Amylases↗
PubMed1978

Diffuse interstitial pneumonitis. Clinicopathologic correlations in 20 patients treated with prednisone/azathioprine.

Twenty patients with diffuse interstitial pulmonary disease diagnosed by open lung biopsy received combined prednisone/azathioprine therapy. Twelve patients demonstrated improvement with therapy. Each patient's clinical presentation, roentgenologic features and pathologic findings were correlated with their therapeutic response. Patients with an illness of one year's duration or less had a more favorable response to therapy than patients with a greater than two year duration of illness. Patients with associated extrathoracic abnormalities (anemia, glomerulitis, hepatopathy) exhibited a better therapeutic response that those with only pulmonary disease. The biopsy material from each patient was quantitatively graded on 20 morphologic variables. Statistical analysis using multiple linear regression revealed that a single variable, degree of interstitial fibrosis, was more that 90 per cent accurate in separating those responsive to therapy from those who failed to respond. Patients who respond to treatment had less interstitial fibrosis. Neither the amount of alveolar septal inflammation nor intra-alveolar cellular reaction was discriminatory in predicting response to therapy. A beneficial response to therapy was reflected in both improved lung volumes and gas exchange. Eight patients appeared to have a selective beneficial effect from azathioprine.

Adult↗
PubMed1978

Repetitive attack by Aspergillus oryzae alpha amylase.

The action of Aspergillus oryzae alpha amylase on reducing-end, and uniformly radiolabeled maltotriose through maltodecaose has been studied. The enzyme is found to hydrolyze more than a single glycosidic bond during enzyme-substrate encounters. The extent of this repetitive attack is quantitated.

Amylases↗
PubMed1978

Actions of lidocaine on transmembrane potentials of subendocardial Purkinje fibers surviving in infarcted canine hearts.

We compared the effects of lidocaine, 2 X 10(-5) M, on transmembrane resting and action potentials of Purkinje fibers on the endocardial surface of 24- to 72-hour-old myocardial infarcts in dogs with its actions and subendocardial Purkinje fibers in normal hearts. At both proximal (near the tip of the papillary muscle) and distal (toward the apex) recording sites in noninfarcted hearts, lidocaine had no significant effect on maximum diastolic potential (MDP) or Vmax. It shortened action potential duration (APD) only at the proximal site. In infarcted hearts, we arbitrarily divided Purkinje fibers at the infarcted distal site into two groups. Group I consisted of fibers which did not have a severely depressed MDP or Vmax but in which APD was markedly prolonged. Lidocaine had no effect on MDP of these fibers, significantly depressed Vmax, and shortened APD. Group II consisted of fibers in which MDP and Vmax were markedly reduced. Lidocaine also reduced Vmax of these fibers further (by 60%) without altering resting potential. In addition, lidocaine depressed pacemaker activity of Purkinje fibers in infarcts. The drug did not alter conduction of premature impulses in the subendocardial Purkinje network in normal hearts but increased the maximum delay of early premature impulses in Purkinje fibers in infarcted hearts and sometimes resulted in nondriven repetitive activity. Therefore, the effects of lidocaine on transmembrane potentials of Purkinje fibers in infarcts are different from its effects on fibers in normal hearts.

Action Potentials↗
PubMed1978

Schedule-induced drinking as functions of interpellet interval and draught size in the Java macaque.

Three Java monkeys received food pellets that were assigned by both ascending and descending series of fixed-time schedules whose values varied between 8 and 256 seconds. The draught size dispensed by a concurrently available water-delivery tube was systematically varied between 1.0 and 0.3 milliliter per lick at various fixed-time values during the second and third series determinations. Session water intake was bitonically related to the interpellet interval and was determined by the interaction of (1) the probability of initiating a drinking bout, which fell off at the highest interpellet intervals and, (2) the size of the bout, which increased directly with increases in interpellet interval. Variations in draught size had little effect on total session intakes, but reduced bout size at draught sizes of 0.5 milliliter and below. Thus, a volume-regulation process of schedule-induced drinking operated generally at the session-intake level, but was limited to higher draught sizes at the bout level.

Journal Article↗
PubMed1977

The effects of heart rate, myocardial ischemia and vagal stimulation on the threshold for ventricular fibrillation.

The minimum current required to cause ventricular fibrillation was determined by electrical stimulation of the normal or ischemic canine left ventricle. The threshold for ventricular fibrillation in the normal heart decreased when the heart rate was rapid. Strong vagal stimulation did not affect the ventricular fibrillation threshold when the heart rate was fixed. The fall in the ventricular fibrillation threshold in the presence of acute myocardial ischemia was greater and more prolonged when the heart rate was rapid. These findings indicate the importance of the immediate correction of tachycardia in patients suffering from acute myocardial infarction.

Animals↗
PubMed1976

Subsite mapping of enzymes. Depolymerase computer modelling.

We have developed a depolymerase computer model that uses a minimization routine. The model is designed so that, given experimental bond-cleavage frequencies for oligomeric substrates and experimental Michaelis parameters as a function of substrate chain length, the optimum subsite map is generated. The minimized sum of the weighted-squared residuals of the experimental and calculated data is used as a criterion of the goodness-of-fit for the optimized subsite map. The application of the minimization procedure to subsite mapping is explored through the use of simulated data. A procedure is developed whereby the minimization model can be used to determine the number of subsites in the enzymic binding region and to locate the position of the catalytic amino acids among these subsites. The degree of propagation of experimental variance into the subsite-binding energies is estimated. The question of whether hydrolytic rate coefficients are constant or a function of the number of filled subsites is examined.

Amino Acid Sequence↗
PubMed1976

Subsite mapping of enzymes. Application of the depolymerase computer model to two alpha-amylases.

In the preceding paper (Allen and Thoma, 1976) we developed a depolymerase computer model, which uses a minimization routine to establish a subsite map for a depolymerase. In the present paper we show how the model is applied to experimental data for two alpha-amylases. Michaelis parameters and bond-cleavage frequencies for substrates of chain lengths up to twelve glucosyl units have been reported for Bacillus amyloliquefaciens, and a subsite map has been proposed for this enzyme [Thoma et al. (1971) J. Biol. Chem. 246, 5621-5635]. By applying the computer model to the experimental data, we have arrived at a ten-subsite map. We find that a significant improvement in this map is achieved by allowing the hydrolytic rate coefficient to vary as a function of the number of occupied subsites comprising the enzyme-binding region. The bond-cleavage frequencies, the enzyme is found to have eight subsites. A partial subsite map is arrived at, but the entire binding region cannot be mapped because Michaelis parameters are complicated by transglycosylation reactions. The hydrolytic rate coefficients for this enzyme are not constant.

Amino Acid Sequence↗
PubMed1976

Acquisition of schedule-induced polydipsia in rats with no prior drinking experience.

Three litters of 10 rat pups each were reared on Purina laboratory chow and either (1) continuous access to water, (2) access to both water and lettuce until weaning at 21 days and then only lettuce, or (3) continuous access to lettuce. At 100 days all rats were reduced to 80% free feeding weight and tested for polydipsia. During 15 sessions of polydipsia testing, excessive postpellet drinking developed in all groups to 45 mg Noyes pellets delivered on a fixed-time 1 min schedule. No significant differences in water intake over sessions were found among groups. It was concluded that schedule-induced polydipsia does not represent an exaggeration of a learned prandial drinking pattern, but rather an exaggeration of an inborn prandial drinking reflex.

Animals↗