Light dependence of the decay of the proton gradient in broken chloroplasts

The initial rates and steady-state values of proton uptake by broken chloroplasts have been measured as functions of light intensity at various concentrations of chlorophyll, pyocyanine, supporting electrolyte, buffer, as well as pH and temperature. Kinetics analysis of the data shows that the rate of decay of proton gradient due to backward leakage depends on light intensity. Under steady illumination, the decay constant kL is equal to kD + mR0, where R0 is the initial rate of proton uptake which is a function of light intensity, kD is the decay constant in the dark and m is a parameter which is independent of light intensity. Treatment of chloroplasts with lysolecithin, neutral detergent, 2,4-dinitrophenol, or valinomycin in the presence of K+ increases kD without affecting m. Treatment with N,N'-dicyclohexylcarbodiimide or adenylyl imidodiphosphate under appropriate conditions decreases m without affectsity and hence m = 0. These results suggest that the light-dependent part (mR0) of kL is due to leakage of protons through the coupling factor (CF1-CF0) complex which can open or close depending on light intensity and that the light independent part (kD) of the decay constant kL is due to proton leakage elsewhere.

alpha-(2-Pyridine)benzyl aryl ketones as potential hypocholesteremic agents

A series of alpha-(2-pyridine)benzyl aryl ketones were prepared as potential hypocholesteremic agents. The synthesis of these compounds was by conversion of 2-benzylpyridine to its anion with n-butyllithium and condensation of the anion with selected aromatic esters. The ketones were tested for their hypocholesteremic activity in rats, and those compounds showing activity were further tested for estrogenicity. Only those aryl ketones with substituents in the ortho position showed a statistically significant reduction in serum cholesterol. Of these compounds the tert-butyl derivative had the most favorable hypocholesteremic to estrogenic ratio.

Purification of the heat-stable inhibitor protein of the Ca2+-activated cyclic nucleotide phosphodiesterase by affinity chromatography

The recently discovered heat-stable inhibitor protein of the Ca2+-activated cyclic nucleotide phosphodiesterase (Sharma, R. K., Wirch, E. & Warg, J. H. (1978) J. Biol. Chem., in press) has been purified 238 214-fold from bovine brain extract using an affinity column of the modulator protein--Sepharose 4B conjugate. The purified sample appears to be homogeneous as judged by sodium dodecyl sulphate (SDS) gel electrophoresis. The protein band has a mobility corresponding to that of a polypeptide of molecular weight 68 000. Since the heat-stable inhibitor protein has a molecular weight of 70 000 under nondenaturing conditions, it suggests that it is a monomeric protein. The protein has no inhibitory activity toward the cAMP-dependent protein kinase or protein phosphatase. The purified sample has been tested for various enzyme activities which include ATPase, GTPase, cAMP phosphodiesterase, cGMP phosphodiesterase, 5'-nucleotidase, and protein kinase. None of these activities are exhibited by the purified sample.

The modulator-dependent protein kinase. A multifunctional protein kinase activatable by the Ca2+-dependent modulator protein of the cyclic nucleotide system

A protein kinase which depends on the simultaneous presence of Ca2+ and the modulator protein for its histone phosphorylation activity has been demonstrated in rabbit skeletal muscle and partially purified. The purified enzyme was not activated by cAMP, cGMP, or incubation with trypsin. Nor was the enzyme inhibited by the protein inhibitor of cAMP-dependent protein kinase. In addition to histone, myosin light chains and phosphorylase kinase served as substrates for the protein kinase, and their phosphorylation also depended on the presence of Ca2+ and the modulator protein. The phosphorylation of phosphorylase kinase was accompanied with a marked activation of the enzyme. The results suggest that the protein kinase has multiple functions and may be involved in the mediation of Ca2+ effects in many biological processes. It is proposed that this enzyme be designated as the modulator-dependent protein kinase. The modulator-dependent protein kinase may be identical to the myosin light chain kinase; chicken gizzard light chain kinase has been shown activatable by the modulator protein (Dabrowska, R., Sherry, J. M. F., Aramatorio, D. K., and Hartshorne, D. J. (1978) Biochemistry 17, 253-258).

Inhibition of Ca2+-activated cyclic nucleotide phosphodiesterase reaction by a heat-stable inhibitor protein from bovine brain

An inhibitor protein of cyclic nucleotide phosphodiesterase is demonstrated in bovine brain extract and separated from modulator binding protein, a recently discovered inhibitory factor of phosphodiesterase. The new inhibitor protein is similar to the cyclic AMP phosphodiesterase inhibitor from bovine retina (Dumler, I. L., and Etingof, F. N. 1976) Biochim. Biophys, Acta 429, 474-484) in its heat stability: it retains full activity upon heating in a boiling water bath for 2 min. The new inhibitor protein counteracts the activation of the Ca2+-activatable cyclic nucleotide phosphodiesterase by the Ca2+-dependent modulator protein without affecting the basal activity of the enzyme. The inhibition of phosphodiesterase by the inhibitor can be reversed by high concentrations of modulator protein but is not influenced by a 20-fold increase in Ca2+ concentration. In contrast, a Ca2+-independent form of cyclic nucleotide phosphodiesterase is not inhibited by the inhibitor protein. These results suggest that the heat-stable inhibitor protein is specific against the action of the Ca2+-dependent modulator protein. Gel filtration analyses on Sephadex G-75 and G-100 columns have shown that the inhibitor protein and the modulator protein may associate in the presence of Ca2+. The molecular weights determined by the gel filtration for the free inhibitor protein and the complex of the inhibitor and modulator protein are about 70,000 and 85,000, respectively.

Purification and characterization of a Ca2+-binding protein in Lumbricus terrestris

A Ca2+-binding protein which is capable of activating mammalian Ca2+-activatable cyclic nucleotide phosphodiesterase has been purified from Lumbricus terrestris and characterized. This protein and the Ca2+-dependent protein modulator from bovine tissues have many similar properties. Both proteins have molecular weights of approximately 18,000, isoelectric points of about pH 4, similar and characteristic ultraviolet spectra, and similar amino acid compositions. Both proteins bind calcium ions with high affinity. However, the protein from Lumbricus terrestris binds 2 mol of calcium ions with equal affinity, Kdiss = 6 X 10(-6) M, whereas the Ca2+-dependent protein modulator from bovine tissues binds 4 mol of calcium ions with differing affinities. Although the Ca2+-binding protein of Lumbricus terrestris activates the Ca2+-activatable cyclic nucleotide phosphodiesterase from mammalian tissues, we have failed to detect the existence of a Ca2+-activatable phosphodiesterase activity in Lumbricus terrestris. The activation of phosphodiesterase by the Ca2+-binding protein from Lumbricus terrestris is inhibited by the recently discovered bovine brain modulator binding protein (Wang, J. H., and Desai, R. (1977) J. Biol. Chem. 252, 4175-4184). Since the modulator binding protein has been shown to associate with the mammalian protein modulator to result in phosphodiesterase inhibition, it can be concluded that the Lumbricus terrestris Ca2+-binding protein also associates with the bovine brain modulator binding protein. Attempts to demonstrate the existence of a similar modulator binding protein in Lumbricus terrestris have been unsuccessful.

Effect of Mg2+ concentration on the cAMP-dependent protein kinase-catalyzed activation of rabbit skeletal muscle phosphorylase kinase

Phosphorylase kinase was found to be activated and phosphorylated at 10mM Mg2+ by the cAMP-dependent protein kinase-catalyzed reaction ot much higher levels than observed previously when reactions were carried out in 1 to 2 mM Mg2+ (Cohen, P. (1973) Eur. J. Biochem. 34, 1; Hayakawa, T., Perkin, J.P., and Krebs, E.G. (1973) Biochemistry 12, 574). That the reaction at 10 mM Mg2+ is protein kinase-catalyzed is supported by several observations: (a) the reaction is facilitated by the addition of protein kinase; (b) the reaction depends on cAMP when protein kinase holoenzyme is uded; (c) the reaction is not inhibited by 1 mM ethylene glycol bis(beta-aminoethyl ether) N,N'-tetraacetate which is known to inhibit autoactivation and autophosphorylation of phosphorylase kinase; and (d) the protein inhibitor of protein kinase inhibits this reaction. The phosphorylation and activation of phosphorylase kinase seem to occur in two phases. At low Mg2+ only the first phase is manifested and involves the incorporation of 2 mol of phosphate, 1 mol into each of Subunits A and B. At high Mg2+ additional sites are phosphorylated almost exclusively on Subunit A, with phosphate incorporation approaching the final level of 7 to 9 mol. Enzyme activity at high Mg2+ is 2 to 3 times higher than that observed when activation is studied at low Mg2+. The observation that both casein and type II histone are phosphorylated to the same extent at 1 mM and 10 mM Mg2+ suggested that high Mg2+ may be altering the conformation of phosphorylase kinase thus rendering more phosphorylation sites accessible to protein kinase. Since the phosphorylation of phosphorylase kinase by either the protein kinase-catalyzed or autocatalytic reaction can result in the incorporation of 7 to 9 mol of phosphate, the finding that only about seven sites become phosphorylated by both mechanisms acting together suggest that activation by these two mechanisms may involve common phosphorylation sites.

Purification of a Ca2+-activatable cyclic nucleotide phosphodiesterase from bovine heart by specific interaction with its Ca2+-dependent modulator protein

A Ca2+-activatable cyclic nucleotide phosphodiesterase from bovine heart can be eluted from a DEAE-cellulose column either in the free form by buffers containing 0.1 mM ethylene glycol bis(beta-aminoethyl ether)N-N,N'N'-tetraacetic acid (EGTA) or as a complex of the enzyme with its protein modulator by buffers containing 0.01 mM CaCl2. A purification procedure based primarily on the significantly different affinity of the two forms of the enzyme for DEAE-cellulose was developed for the purification of the enzyme from bovine heart. The procedure involves ammonium sulfate fractionation, three chromatographic steps on DEAE-cellulose, and gel filtration on Sephadex G-200 with a 5000-fold purification over the crude extract. The purified enzyme has a specific activity of 120 mumol of cAMP/mg/min, can be activated 5-fold by Ca2+, but is only 80% pure as judged by analytical disc gel electrophoresis. The purified enzyme is unstable but can be stabilized by addition of Ca2+ and the protein modulator; this is in contrast to the less pure preparations of Ca2+-activatable phosphodiesterase which are destabilized by the protein modulator in the presence of Ca2+.

Comparison of calcium-binding proteins. Bovine heart and brain protein activators of cyclic nucleotide phosphodiesterase and rabbit skeletal muscle troponin C

In previous studies we have shown that the activation of bovine heart cyclic nucleotide phosphodiesterase by purified protein activator is completely dependent on the presence of Ca2+ and that the protein activator Ca2+ complex is probably the true activator for the enzyme (Teo, T.S. and Wang, J.H. (1973) J. Biol. Chem. 248, 5930-5955). More recent studies have led us to believe that the mechanism of the Ca2+ activation of phosphodiesterase resembles that of the Ca2+ activation of muscle contraction and that the protein activator may play a role similar to troponin. In the present study we show that the protein activator resembles rabbit muscle troponin C in amino acid composition, molecular weight, isoelectric point, and ultraviolet absorption spectrum. Preliminary structural studies also indicate that these two proteins may have evolved from a common ancestral protein through gene duplication. This argument is strengthened by the finding that the tryptic peptide map of the bovine heart protein activator is indistinguishable from that of the bovine brain phosphodiesterase activator protein for which preliminary sequence information also suggests homology to troponin C (Watterson, D.M., Harrelson, W.G., Jr., Keller, P.M., Sharief, F., and Vanaman, T.C. (1976) J. Biol. Chem. 251, 4501-4513).

A study on the autoactivation of rabbit muscle phosphorylase kinase

Under conditions favoring its autocatalytic reaction, phosphorylase kinase may be activated and phosphorylated in 2-(N-morpholino)ethanesulfonate (Mes) buffer to a much higher level than in beta-glycerophosphate buffer. The fact that the reaction is autocatalytic is supported by several observations: (a) the progress curve of the reaction exhibits a pronounced lag phase, (b) the reaction is strongly inhibited by ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetate, which inhibits phosphorylase kinase, (c) the pH profile of the reaction resembles that of the phosphorylase b to a reaction as catalyzed by nonactivated phosphorylase kinase, and (d) the reaction is not significantly affected by adenosine 3':5'-monophosphate (cAMP) nor by the heat-stable protein inhibitor of cAMP-dependent protein kinases. When fully autoactivated, phosphorylase kinase possesses an activity that is 100% higher than that of the protein kinase-activated form. The results suggest that autophosphorylation of phosphorylase kinase may be an important regulatory mechanism. The autocatalytic reaction involves phosphorylation of the two larger subunits of phosphorylase kinase, i.e. subunits A and B, with a combined total of 7 to 9 phosphates incorporated per mol of enzyme. Although the cAMP-dependent protein kinase also catalyzes the phosphorylation of subunits A and B, the two mechanisms of phosphorylation appear to involve different sites. Prior phosphorylation of phosphorylase kinase by the protein kinase has little effect on the level of autophosphorylation. Thus activation of phosphorylase kinase may be brought about by phosphorylation of the enzyme at different sites.

Chemical models of oxidative phosphorylation

Chemical models for coupling oxidation to phosphorylation are summarized and examined both from the standpoint of organic reaction mechanisms and with respect to their relevance to mitochondria and chloroplasts. In order to accelerate the progress of our research in bioenergetics, it is suggested to focus at least as much attention on structural biochemistry as on phenomenological observations of energy-transducing membranes.

Ridge augmentation: an evaluation and follow-up report

An evaluation was made of results of follow-up studies, ranging from nine months to about 3 1/2 years, of six patients who had mandibular ridge augmentations at the University of Minnesota Hospitals. Clinical observations, patients' subjective feelings, and measurements of vertical loss of the original graft were the main considerations in the studies. Although there was almost continual resorption of the bone grafts after surgery patients were satisfied with the procedure and the current dental function.

Catalytic and regulatory properties of two forms of bovine heart cyclic nucleotide phosphodiesterase

The soluble supernatant fraction of bovine heart homogenates may be fractionated on a DEAE cellulose column into two cyclic nucleotide phosphodiesterases (EC 3.1.4.-):PI and PII phosphodiesterases, in the order of emergence from the column. In the presence of free Ca2+, the PI enzyme may be activated several fold by the protein activator which was discovered by Cheung((1971) J. Biol. Chem. 246, 2859-2869). The PII enzyme is refractory to this activator, and is not inhibited by the Ca2+ chelating agent, ethylene glycol bis (beta-aminoethyl ether)-N, N'-tetraacetate (EGTA). The activated activity of PI phosphodiesterase may be further stimulated by imidazole or NH+4, and inhibited by high concentrations of Mg2+. These reagents have no significant effect on either the PII enzyme or the basal activity of PI phosphodiesterase. Although both forms of phosphodiesterase can hydrolyze either cyclic AMP or cyclic GMP, they exhibit different relative affinities towards these two cyclic nucleotides. The PI enzyme appears to have much higher affinities toward cyclic GMP than cyclic AMP. Km values for cyclic AMP and cyclic GMP are respectively 1.7 and 0.33 mM for the non-activated PI phosphodiesterase; and 0.2 and 0.007 mM for the activated enzyme. Each cyclic nucleotide acts as a competitive inhibitor for the other with Ki values similar to the respective Km values. In contrast with PI phosphodiesterase, PII phosphodiesterase exhibits similar affinity toward cyclic AMP and cyclic GMP. The apparent Km values of cyclic AMP and cyclic GMP for the PII enzyme are approx. 0.05 and 0.03 mM, respectively. The kinetic plot with respect to cyclic GMP shows positive cooperativity. Each cyclic nucleotide acts as a non-competitive inhibitor for the other nucleotide. These kinetic properties of PI and PII phosphodiesterase of bovine heart are very similar to those of rat liver cyclic GMP and high Km cyclic AMP phosphodiesterases, respectively (Russel, Terasaki and Appleman, (1973) J. Biol. Chem. 248, 1334).

Equilibrium potentials of membrane electrodes

A simple thermodynamic theory of the equilibrium potentials of membrane electrodes is formulated and applied to the glass electrode for measurement of pH. The new formulation assumes the selective adsorption or binding of specific ions on the surface of the membrane which may or may not be permeable to the ion, and includes the conventional derivation based on reversible ion transport across membranes as a special case. To test the theory, a platinum wire was coated with a mixture of stearic acid and methyl-tri-n-octyl-ammonium stearate. When this coated electrode was immersed in aqueous phosphate solution, its potential was found to be a linear function of pH from pH 2 to 12 with a slope equal to the theoretical value of 59.0 mV per pH unit at 24 degrees .