Inactivation of phosphofructokinase 2 by cyclic AMP - dependent protein kinase

Treatment with the catalytic subunit of cyclic AMP-dependent protein kinase induced the following modifications in the kinetic properties of purified phosphofructokinase 2. The affinity for Fru-6-P, the V_max and the stimulatory effect of P_i were decreased; the inhibitory actions of P-enol-pyruvate and citrate were increased; the pH activity curve, measured in the presence of 5 mM Fru-6-P and 5 mM P_i was modified in the respect that the peak of activity normally measured at pH 6.6 was abolished whereas no effect of the treatment was observed at pH 8. Similar changes in the properties of phosphofructokinase 2 were also observed in a crude preparation obtained from hepatocytes incubated with glucagon.     

The reaction between cytochrome c1 and cytochrome c

The kinetics of electron transfer between the isolated enzymes of cytochrome c1 and cytochrome c have been investigated using the stopped-flow technique. The reaction between ferrocytochrome c1 and ferricytochrome c is fast; the second-order rate constant (k1) is 3.0 . 10(7) M-1 . s-1 at low ionic strength (I = 223 mM, 10 degrees C). The value of this rate constant decreases to 1.8 . 10(5) M-1 . s-1 upon increasing the ionic strength to 1.13 M. The ionic strength dependence of the electron transfer between cytochrome c1 and cytochrome c implies the involvement of electrostatic interactions in the reaction between both cytochromes. In addition to a general influence of ionic strength, specific anion effects are found for phosphate, chloride and morpholinosulphonate. These anions appear to inhibit the reaction between cytochrome c1 and cytochrome c by binding of these anions to the cytochrome c molecule. Such a phenomenon is not observed for cacodylate. At an ionic strength of 1.02 M, the second-order rate constants for the reaction between ferrocytochrome c1 and ferricytochrome c and the reverse reaction are k1 = 2.4 . 10(5) M-1 . s-1 and k-1 = 3.3 . 10(5) M-1 . s-1, respectively (450 mM potassium phosphate, pH 7.0, 1% Tween 20, 10 degrees C). The 'equilibrium' constant calculated from the rate constants (0.73) is equal to the constant determined from equilibrium studies. Moreover, it is shown that at this ionic strength, the concentrations of intermediary complexes are very low and that the value of the equilibrium constant is independent of ionic strength. These data can be fitted into the following simple reaction scheme: cytochrome c2+1 + cytochrome c3+ in equilibrium or formed from cytochrome c3+1 + cytochrome c2+.     

Primary structure of the asparagine-563-linked carbohydrate chain of an immunoglobulin M from a patient with Waldenstrom's macroglobulinemia. A reinvestigation by 500-MHz H-NMR spectroscopy

The activity of microsomal cholesterol 7α-hydroxylase is shown to be increased in vitro by ATP, Mg²⁺, and a cytosolic protein fraction. There was a loss of enzyme activity in the presence of E. coli alkaline phosphatase which was proportional to the amount of phosphatase. Much of this loss was recovered upon addition of ATP, Mg²⁺, and a cytosolic protein fraction.     

The fraction of phosphatidylinositol that activates the (Na+ + K+)-ATPase in rabbit kidney microsomes is clearly associated with the enzyme protein

1. Extensive treatment of rabbit kidney microsomes with phosphatidylinositol-specific phospholipase C under various conditions never resulted in more than 75% hydrolysis of the substrate. 2. The non-degraded fraction of the phosphatidylinositol (10-12 nmol per mg microsomal protein) could be recovered only by an acidic extraction procedure. 3. The (Na+ + K+)-ATPase activity found in those membranes was not affected by this treatment. 4. Complete degradation of phosphatidylinositol could be easily achieved when the phospholipase was applied to rat liver microsomes which do not contain any detectable (Na+ + K+)-ATPase activity. 5. It is concluded that in rabbit kidney microsomes a close association exists between the (Na+ + K+)-ATPase and that fraction of the phosphatidylinositol that is directly involved in the maintenance of its activity.     

Acoustic modes and nonbonded interactions of the double helix

Observations of acoustic velocities in DNA fibers have been used to refine nonbonded force constants for the DNA double helix. Long-range forces are found to be needed for A conformation and are likely to dominate in B conformation as well. The acoustic dispersion curves are described and calculated. A correction due to the effects of water is calculated. The effect of nonbonded interaction on other vibrational modes is calculated.     

Plasmodium falciparum: Synthesis of glycoprotein by cultured erythrocytic stages

The human malarial parasite, Plasmodium falciparum, incorporated significant radioactivity into glycoconjugates when cultured in the presence of [¹⁴C]- or [³H]glucosamine for 48 to 50 hr. Digestion of the labeled proteins with pronase and subsequent precipitation with absolute ethanol showed that 90 to 95% of the radioactive glucosamine was incorporated into the precipitated material. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the labeled macromolecules revealed eight bands with approximate molecular weights from 19,000 to 90,000 daltons.     

Dynamic geometry of the intact left ventricle

Knowledge of left ventricular chamber dynamics is central to our understanding of cardiac physiology. The complicated changes in left ventricular geometry observed in the dog during various phases of the cardiac cycle can be represented as distinct linear relationships between chamber eccentricity and intracavitary volume during diastole and ejection, and probably represent structural properties of the ventricular wall. Chamber geometry of the left ventricle is a major determinant of overall myocardial function. The slope of the radius of curvature (r) to wall thickness (h) relationship is a geometric constant that determines the mural force at any given transmural pressure. Chronic pressure and volume overload produce changes in this geometric relationship as a result of increased mural force resisting ejection. The adaptive mechanism of ventricular hypertrophy in this setting alters the r/h ratio and returns systolic mural force toward normal. Coronary occlusion induces acute changes in regional geometry characterized by holosystolic wall bulging and systolic wall thinning, which shift the r/h relationship upward and to the left. The geometric alteration during ischemia probably increases systolic mural force and could adversely affect myocardial function. Recent studies with patients have shown the r/h ratio to be of value in distinguishing between reversible and irreversible impairment of myocardial performance. Because most myocardial diseases produce major alterations in the structure of the ventricular wall, analysis of dynamic chamber geometry may prove of prognostic value in assessing patients with cardiac disorders.