A third DNA polymerase from Spiroplasma citri and two other spiroplasmas.

Recently, two DNA polymerases (ScA and ScB) were isolated and characterized from Spiroplasma citri. We now have found a third DNA polymerase (ScC) not only in S. citri but also in the serologically related honeybee spiroplasma BC3 and the unrelated flower spiroplasma BNR1. Enzyme ScC is N-ethylmaleimide (NEM) sensitive. The three DNA polymerases from the honeybee spiroplasma seem to be similar to the respective enzymes of S. citri. However, whereas the NEM-resistant enzyme ScA from S. citri and that from the BC3 honeybee spiroplasma are retained on DEAE-cellulose and require 0.09 M KCl for elution, the NEM-resistant enzyme A from the flower spiroplasma BNR1 is not retained.     

Separation and partial characterization of two deoxyribonucleic acid polymerases from Spiroplasma citri.

The separation and partial characterization of two deoxyribonucleic acid polymerases from Spiroplasma citri have been achieved. The two enzymes had different elution properties on diethylaminoethyl (DEAE) cellulose and differed in their sensitivity to N-ethylmaleimide (NEM), preference for different template-primers, and sedimentation velocity in linear glycerol gradients. The first enzyme activity, ScA, was retained on DEAE-cellulose and was not inhibited by NEM. Activated deoxyribonucleic acid and poly(dA)-oligo(dT12) were the preferred template-primers. Arabinosyl-cytidine triphosphate had no effect. The sedimentation coefficient of ScA was 6.3s. The second activity, ScB, was not retained on DEAE-cellulose and was inhibited by NEM. Poly(dA)-oligo(dT12) was the preferred template-primer, whereas activated DNA was only poorly utilized. ScB was not affected by arabinosyl-cytidine triphosphate, and its sedimentation coefficient was 4.4s. The polymerization activities of the two enzymes were maximum at 37 to 40 degrees C.     

Polarization of Myosin II Refines Tissue Material Properties to Buffer Mechanical Stress

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Modeling of the Norwood circulation: effects of shunt size, vascular resistances, and heart rate

Hypoplastic left heart syndrome is the most common lethal cardiac malformation of the newborn. Its treatment, apart from heart transplantation, is the Norwood operation. The initial procedure for this staged repair consists of reconstructing a circulation where a single outlet from the heart provides systemic perfusion and an interpositioning shunt contributes blood flow to the lungs. To better understand this unique physiology, a computational model of the Norwood circulation was constructed on the basis of compartmental analysis. Influences of shunt diameter, systemic and pulmonary vascular resistance, and heart rate on the cardiovascular dynamics and oxygenation were studied. Simulations showed that 1) larger shunts diverted an increased proportion of cardiac output to the lungs, away from systemic perfusion, resulting in poorer O2 delivery, 2) systemic vascular resistance exerted more effect on hemodynamics than pulmonary vascular resistance, 3) systemic arterial oxygenation was minimally influenced by heart rate changes, 4) there was a better correlation between venous O2 saturation and O2 delivery than between arterial O2 saturation and O2 delivery, and 5) a pulmonary-to-systemic blood flow ratio of 1 resulted in optimal O2 delivery in all physiological states and shunt sizes.