Effect of (+)-cyanidanol-3 on chronic active hepatitis: a double blind controlled trial

Forty patients with biopsy proven chronic active hepatitis were studied, 22 received (+)-cyanidanol-3 in a dose of 3 g daily and 18 placebo. Side effects related to cyanidanol were fever (four patients), haemolysis (one patient) and urticaria (one patient). All side effects subsided on discontinuation of the medication. Cyanidanol had an effect no better than placebo on symptoms, laboratory tests, and histological findings on liver biopsy.

Acral (volar-subungual) melanoma

Acral melanoma occurs in the volar surface of the hands, feet, fingers, toes and subungual sites. Recently it has been recognized as a distinct entity with characteristic clinical and pathological features. Of our 340 patients with malignant melanoma, 24 (7 per cent) had acral melanoma. Sixteen were in the plantar skin, two in the palms and six in the nailbed. The delay in diagnosis was 6 months to 5 years and most of the patients presented with large neglected tumours. Fourteen lesions had histological features consistent with acral lentiginous melanoma - a unique pattern to this area. Fourteen patients were in clinical stage I at diagnosis, seven in stage II and three had distant metastases (stage III). The treatment was mainly surgical. Palmar-plantar lesions were widely excised. One patient underwent below-knee amputation. Lesions of the digits were treated by amputation of the affected toe. Fourteen of the patients underwent either prophylactic or therapeutic lymph node dissection. In 9 of them, regional metastases were found. In patients with advanced disease chemotherapy was added. Three patients had isolated limb perfusion. Fourteen patients died of metastatic disease within 1-5 years. Four are alive but have metastatic spread. Six patients are disease-free, one to 4.5 years following diagnosis.

Effect of buffer on kinetics of proton equilibration with a protonable group

The laser-induced proton pulse generates a massive, brief, proton pulse capable of perturbing biochemical equilibria. The time resolution of the monitoring system can follow the diffusion-controlled protonation of specific sites on macromolecular bodies [Gutman, M. (1984) Methods Biochem. Anal. 30, 1-103]. In order to apply this method in enzymology, one must first evaluate how the buffer capacity of biochemical systems (substrates and proteins) will affect the observed dynamics. Unlike equilibrium measurements, where buffer is an inert component, in kinetic studies buffer modulates the observed dynamics. In this paper we analyze the effect of buffer on the dynamics of protonation in a model system. We describe the experimental technique and introduce the mathematical formalism that determines the various rate constants involved in the reaction. The analysis of the experiments indicates that in buffered solution proton flux is carried by two mechanisms: (A) proton dissociation followed by free proton diffusion; (B) collisional proton transfer between small diffusing solutes. We demonstrate how to evaluate the contribution of each pathway to the overall proton flux.

Kinetic analysis of protonation of a specific site on a buffered surface of a macromolecular body

The kinetics of protonation of a specific site on a macromolecular structure (micelle) in buffered solution was studied with the purpose of evaluating the effect of buffer on the observed dynamics. The experimental system consisted of the following elements: Brij 58 micelles serving as homogeneous uncharged macromolecular bodies, bromocresol green, a well-adsorbed proton detector, and 2-naphthol-3,6-disulfonate as a proton emitter in the bulk. Imidazole was the mobile buffer while neutral red, which has a high affinity for the micellar surface, served as the immobile buffer. An intensive laser pulse ejects a proton from the proton emitter, and the subsequent proton-transfer reactions are measured by fast spectrophotometric methods. The dynamics of proton pulse in buffered solution are characterized by a very rapid trapping of the discharged protons by the abundant buffer molecules. This event has a major effect on the kinetic regime of the reaction. During the first 200 ns the proton flux is rate limited by free-proton diffusion. After this period, when the free-proton concentration decayed to the equilibrium level, the relaxation of the system is carried out by the diffusion of buffer. Thus in the buffered biochemical system, at neutral pH, most of proton flux between active sites and bulk is carried out by buffer molecules--not by diffusion of free protons. Surface groups on a high molecular weight body exchange protons among them at a very fast rate. This reaction has a major role on proton transfer from a specific site to the bulk.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic analysis of proton transfer between reactants adsorbed to the same micelle. The effect of proximity on the rate constants

The dense packing of protogenic enzymes on the coupling membrane can furnish a route for a rapid proton flux which may avoid the adjacent bulk phase. In order to evaluate the role of proximity between reactants on the rate constant of proton transfer we generated a model system consisting of 2-naphthol and pH indicator (bromocresol green) both adsorbed on the same micelle of unchanged detergent. Excitation of the 2-naphthol by a short intensive laser pulse lowers its pK with subsequent synchronized proton ejection. The discharged protons are detected by their reaction with the indicator using a fast transient absorption technique. Evidence is produced that under certain conditions all of the observed proton flux represents proton transfer between 2-naphthol and indicator molecules sharing the same micelle. In this model system the entire proton flux proceeds through an aqueous phase fully accessible to phosphate ions. The high proximity of the reactants (the separation can not exceed approximately 6 nm) has a marked effect on the rate constant of the reaction k = 2.0 +/- 0.5 X 10(11) M-1 s-1. In spite of this extremely fast rate of reaction we observe unhindered competition, for the surface discharged proton, between the surface-bound reactants and phosphate ions in the bulk. Thus even in proton transfer between closely packed reactants on an interface, the diffusion of the proton is not limited to the interface. This finding implies that on bioenergetic surface the electrochemical potential of the proton on the surface will equal that of the bulk.

Hypothalamic self-stimulation: the role of dopamine and possible relations to neocortical slow wave activity

Reserpine abolishes self-stimulation in rats but the behavior can be restored temporarily by treatment with D-amphetamine or L-DOPA. Apomorphine does not restore self-stimulation even though it restores spontaneous motor activity in reserpinized rats. The data indicate that dopamine plays a role in reinforcement as well as in motor function. The ability of D-amphetamine to restore self-stimulation in reserpinized rats is eliminated by concurrent treatment with atropine or scopolamine. This effect may be related to the presence of continuous large amplitude slow wave activity in the neocortex under these conditions.

Fluorescence decay time measurements of Eu3+-ATP-enzyme complexes. Replacement of the metal hydration water by active site ligands

Measurements of the fluorescent lifetimes of the rare earth metal Eu3+ in varying mole fractions of H2O/D2O were used to determine the hydration of the metal in the presence of ATP and/or hexokinase or chloroplast reversible ATPase. The number of water molecules coordinated to the metal in Eu3+-ATP was estimated to be 2.6; when this complex is bound to hexokinase, 1 water molecule is displaced. Upon binding to chloroplast reversible ATPase, the metal coordinates 1 water molecule while the Eu3+-ATP complex does not retain any associated solvent. These numbers are in contrast to the 9 solvent molecules coordinated to the naked metal ion. These results are discussed in reference to mechanistic and structural considerations of the two enzymes.

Unknown primary melanoma

Of 230 melanoma patients treated during the past 8 years, 12 (5.2%) were found to have unknown primary lesions. Nine of these "unknown primary melanoma' patients presented with metastases in regional lymph nodes, one inside the parotid gland, and two presented with disseminated melanoma and no detectable primary tumor. The patients with melanoma confined to a regional lymph node underwent block dissection followed by adjuvant chemotherapy and immunotherapy. Four patients with metastasis in only one lymph node are disease free 4-6 years after diagnosis. One patient with multiple metastases in the groin is alive 8 years after lymphadenectomy. The other five patients with metastases in multiple regional lymph node died 16 months to 3 years after surgery. Both patients with disseminated melanoma succumbed to their disease within a month of diagnosis. The prognosis of unknown primary melanoma seems to be no worse than the typical melanoma at the same stage. This justifies the aggressive surgical approach to this unusual entity of melanoma.

Kinetic analysis of the protonation of a surface group of a macromolecule

The dynamics of proton transfer between a surface-attached acidic moiety and the bulk of the solution was measured using the laser-induced proton pulse technique. [Gutman, M., Huppert, D. and Pines, E. (1981) J. Am. Chem. Soc. 103, 3709-3713]. The model system for this study consists of pH indicators (either neutral red or bromcresol green) adsorbed on Brij 58 micelles, as defined targets for protonation and a non-adsorbed proton emitter (2-naphthol-3,6-disulfonate) for generation of protons in bulk. The reaction was measured with 50-ns time resolution over a time period of about 200 microseconds. The results were analyzed by a numerical solution of the coupled nonlinear differential equation corresponding with the reaction system. [Gutman, M., et al. (1983) J. Am. Chem. Soc. 105, 2210-2216]. Quantitative analysis reveals two independent reactions which govern the observed dynamics: (a) a diffusion-controlled reaction between the proton and the surface targets; (b) translocation of the protonated target between the hydration layer of the interface and a more hydrophobic one. The contribution of the translocation reaction to the dynamics of surface protonation is more pronounced for compounds like carboxylates or phenolates which increase their hydrophobicity upon protonation. Amines and azoaromatic structures are more hydrophilic in their protonated states, the dynamics of their protonation is less affected by post-protonation distribution within the microenvironments of the interface. The interrelation between the partial rate constants and the macroscopic time constants and equilibrium parameters is analyzed.

Herpes genitalis in patients attending a clinic for sexually transmitted diseases

In a prospective study of 210 patients attending a hospital-based sexually transmitted disease clinic, we documented the prevalence of genital herpes infection (GHI) and its association with gonococcal infection (GI). Herpes simplex virus type 2 was cultured from 58% of symptomatic patients and 0.5% of asymptomatic patients.The ratio of GI to GHI was 41:31 by clinical criteria. The laboratory-confirmed ratio was 41:18. These ratios are much higher than those normally used to estimate the caseload of GHI.

Direct measurement of proton transfer as a probing reaction for the microenvironment of the apomyoglobin heme-binding site

Aromatic alcohols fluoresce at different wavelengths in their neutral (phiOH*) and anionic (phiO-*) excited states. Consequently, time-resolved fluorescence measurements, at the respective wavelengths, can be used for measuring the rates of proton dissociation and recombination of the excited molecule. As the lifetime of the excited state is very short (a few nanoseconds), the measured reaction is that which takes place in a volume corresponding to the diffusion distance of the proton during the lifetime of the excited state. 8-Hydroxypyrene 1,3,6-trisulfonate (pK = 7.7, pK* = 0.5) is bound to apomyoglobin with a stoichiometry of 1:1. In the bound state its neutral form fluorescence increase 20-fold. The binding affinity is pH-dependent. Two protonatable groups, with pK = 6.5, participate in the stabilization of the negatively charged ligand in the binding site. The ligand is bound only to the apoprotein and is displaced from its site by hemin. Thus we suggest that the ligand is bound to the heme binding site of apomyoglobin. Time-resolved fluorescence of the bound ligand yields the rate constants of proton dissociation and recombination as taking place within the heme binding cavity of apomyoglobin. The rate of proton dissociation is slowed to 7% of the rate measured for the free ligand. Such a slow dissociation indicates a strong interaction of the water in the cavity with the walls [Gutman, M., Huppert, D., and Nachliel, E. (1982) Eur. J. Biochem. 121, 637-642]. The water activity in the site is equivalent to alpha (H2O) = 0.67.

Kinetic studies of proton transfer in the microenvironment of a binding site

Excitation of 8-hydroxypyrene 1,3,6-trisulfonate to its first electronic singlet state converts the compound from weak base (pK degrees = 7.7) into a strong acid (pK* = 0.5). The dissociation of the proton in water or dilute salt solution is a very fast reaction, K12 = 1 X 10(10) S-1. In concentrated salt solutions the dissociation is slowed as an exponential function of the chemical activity of the water in the solution. This kinetic parameter has been used to gauge the properties of the microenvironment of the binding sites of bovine serum albumin at which this compound is bound. Time-resolved fluorometry reveals two distinct steps: a rapid dissociation of the proton with tau = 300 +/- 40 ps which lasts approximately 0.5 ns, followed by a slower reaction with tau = 3.3 ns. The first rapid phase represents proton dissociation taking place in the binding site. From the rate constant K = 3.3 X 10(9) s-1 we estimate that the ability of the water molecules in the site to hydrate the ejected proton is equivalent to a salt solution with water activity of 0.85. The slow phase represents the escape of the proton from the binding site. The rate of the escape, 1.4 X 10(8) s-1, is significantly slower than diffusion-controlled dissociation. It is concluded that the shape of the site or its lowered proton conductivity do not allow a rapid escape of the proton to the bulk. Still it should be remembered that the escape of the proton is 10(5)-10(6)-times faster than a typical turnover of an enzyme.U

Modulation by divalent metal ions of the autocatalytic reactivity of adenosinetriphosphatase from chloroplasts

A nonlinear, pre-steady-state initial rate of ATP hydrolysis is obtained on the addition of a divalent metal ion--ATP complex to a heat-activated coupling factor 1 isolated from chloroplasts. The acceleration of the initial rate follows first-order kinetics. The observed first-order kinetic constant (kobsd) changes with the concentration of the substrate, reaching half-maximal value at the Km for ATP hydrolysis. Preincubation of the enzyme with divalent metal ions decreases the kobsd from 1 to 0.04 s-1. Saturation of the divalent metal ion effect was obtained at the micromolar range. It is suggested that the autocatalysis is a result of early stages in ATP hydrolysis which induce conformational changes in the enzyme. Binding of divalent metal ions in the absence of ATP slows down this change.

Probing the micelle/water interface by a rapid laser-induced proton pulse

The laser-induced pH jump (Gutman, M. and Huppert, D.J. (1979) Biochem. Biophys. Methods 1, 9-19) has a time resolution capable of measuring the diffusion-controlled rate constant of proton binding. In the present study we employed this technique for measuring the kinetics of protonation-deprotonation of surface groups of macromolecules. The heterogeneous surface of proteins excludes them from serving as a simple model, therefore we used micelles of a neutral detergent (Brij 58) as a high molecular weight structure. The charge was varied by the addition of a low concentration of sodium dodecyl sulfate and the surface group with which the protons react was an adsorbed pH indicator (bromocresol green or neutral red). The dissociation of a proton from adsorbed bromocresol green is slower than that from free indicator. This effect is attributed to the enhanced stabilization of the acid form of the indicator in the pallisade region of the micelle. The pK shift of bromocresol green adsorbed on neutral micelles is thus quantitatively accounted for by the decreased rate of proton dissociation. Indicators such as neutral red, which are more lipid soluble in their alkaline form, do not exhibit such decelerated proton dissociation in their adsorbed state nor a pK shift on adsorption to neutral micelles. The protonation of an indicator is a diffusion-controlled reaction, whether it is free in solution or adsorbed on micelles. By varying the electric charge of the micelle this rate can be accelerated or decelerated depending on the total charge of the micelle. The micellar charge calculated from this method was corroborated by other measurements which rely only on equilibrium parameters. The high time resolution of the pH jump is exemplified by the ability to estimate the diffusion coefficient of protons through the hydrated shell of the micelle.

Efficacy of Influenza Inoculation: Intradermal versus Subcutaneous Route

Intradermal injection of antigen can theoretically produce the same antibody response as 10-20% of the volume required for subcutaneous injection. This paper demonstrates equal efficacy of intradermal injection of Fluviral vaccine as compared to subcutaneous injection in an ambulatory geriatric population. There was no difference in adverse reactions between the two groups. A significant portion of both groups did not develop protective HAI antibody level to or more than 1/40.

The effect of membrane potential on the redox state of cytochrome b561 in antimycin-inhibited submitochondrial particles

The oxidation of cytochrome b561 by ATP was measured in submitochondrial particles inhibited by antimycin. The redox potential of the bulk (M phase) was controlled by the ratio of fumarate:succinate, and the oxidation of cytochrome b was calculated and expressed as a change in redox potential (Eh) measured in millivolts. The oxidation of cytochrome b561 is an energy-driven reaction affected only by the delta psi component of the proton motive force. The oxidation (measured in millivolts) is a function of the phosphate potential, reaching a maximal value of 40 mV at delta G'ATP less than - 12 kcal/mole. The maximal measured value of ATP-dependent delta psi was 100 mV. Thus only a fraction of the membrane potential effects the redox state of cytochrome b561. In contrast to the ATP-induced oxidation of cytochrome b561, cytochrome b566 is in redox equilibrium with fumarate succinate either in the presence or in the absence of ATP. The selective oxidation of b561 is explained within the term of the Q cycle as a reflection of delta psi on the electron electrochemical potential. The positive electric potential of the C phase causes cytochrome b566 to act as oxidant with respect to cytochrome b561. In the presence of antimycin cytochrome b561 cannot equilibrate with the quinone and undergoes oxidation, while cytochrome b566 reequilibrates with the quinone and thus regains redox equilibrium with the fumarate succinate redox buffer.

Modulation of the flavin redox potential as mode of regulation of succinate dehydrogenase activity

The redox properties of flavin in active and non-active (oxaloacetate reacted) soluble succinate dehydrogenase were studied. Quantitative analysis of reductive activation titrations of redox titrations of active and non-active enzyme reveal that the redox potential of the histidyl-flavin in the active enzyme (-3 +/- 15 mV) is high enough to allow reduction by succinate, whereas in the non active enzyme it is -196 +/- 19 mV, far to low to be reduced by substrate. The flavin radical in the active enzyme attains 60% of total flavin at a poised redox potential of about +60 mV, upon addition of oxaloacetate the magnitude of the signal is diminished and the potential where it reaches maximal concentration is shifted by about -200 mV. A mechanism is proposed which ascribes the fundamental difference between active and non-active enzyme to the inability of the latter to be reduced by substrate.

Rapid pH and deltamuH+ jump by short laser pulse

The excited state (S1) of sulfononaphthols has a pK value well below that of the ground state, consequently intensive illumination of their aqueous solution should lead to acidification. In this study the second harmonies of a ruby laser pulse (10 MW, 30 ns at 347.2 nm) were used for excitation of a sulfononaphthol solution, resulting in a lowering of the pH from 8 to 4. The change in pH was demonstrated by spectral changes of the pH indicators Bromocresol Green, Bromothymol Blue, Bromocresol Purple and Phenol Red. The magnitude of the pH change was calculated from the kinetics of the changes in the indicators' absorbance and from fluorescence intensity of naphtholate. Sulfononaphthols, due to their hydrophylic nature, cannot permeate across phospholipid membranes. Taking advantage of this property, liposomes containing sulfononaphthol were prepared and irradiated by the laser pulse. Evidence is given that under such conditions the change in pH was limited to the space enclosed in the liposomes. The resulting proton-motive force (deltamuH+ = 180 -- 240 mV) is adequate for perturbing the energy-coupled reactions of oxidative phosphorylation. Possible applications of this technique in chemical physics, chemistry, biochemistry and bioenergetics are discussed.

Distinction between NAD- and NADH-binding forms of mitochondrial malate dehydrogenase as shown by inhibition with thenoyltrifuoroacetone

The inhibition of mitochondrial malate dehydrogenase (L-malate : NADH oxidoreductase, EC 1.1.1.37) by 2-thenoyltrifluoroacetone (TTFA) was investigated at pH 8.0 where both forward and backward reactions can be measured. The inhibition with respect to malate is non-competitive at finite NAD concentrations. Increasing the NAD concentrations lowers the slope of the double reciprocal plot so that at infinite NAD the inhibition is uncompetitive. The inhibition with respect to oxaloacetate is non-competitive. Increasing the NADH concentration lowers the slope and intercept of the double reciprocal plot so that at infinite NADH the inhibition is nil. The inhibition with respect to NADH is competitive, whatever the oxaloacetate concentrations are. The inhibition with respect to NAD, at all malate concentrations, is non-competitive. This pattern of inhibition is incompatible with any model assuming that NAD and NADH reacts with identical forms of the enzyme. On the other hand the reciprocating compulsory ordered mechanism, where the two subunits of the dimeric enzyme are working in concert, can account for all the experimental results. It is concluded that NAD and NADH bind to different forms of the enzyme separated by reversible steps. Only one form (see text), the one which binds NADH, can react to form the dead end complex (see text). The similarity between mechanism of inhibition by thenoyltrifluoroacetone and other hydrophobic inhibitors of malate dehydrogenase is discussed.

The effect of opposing effectors on activation level of succinate dehydrogenase: equilibrium and kinetic studies

The activation of mitochondrial succinate dehydrogenase by various activators is a result of dissociation of oxaloacetate tightly bound to the nonactive enzyme. But, quantitative correlation between the effector concentrations and the active fraction of the enzyme was not at hand. In this study we measured the level of active succinate dehydrogenase equilibrated with a wide range of opposing effectors: oxaloacetate (1-500 muM) and activator (0.02-1.5 M NaBr). The results are compatible with a model assuming two stable forms of the enzyme: a nonactive enzyme-oxaloacetate complex and an active enzyme free of oxaloacetate. The active form is stabilized by binding two Br- and one H+. The rate of activation (ka) and exchange between enzyme bound and free oxaloacetate k(ex) were measured. Both ka and kex are hyperbolically dependent on Br- concentration but differ in magnitude and pH dependence. kex at infinite Br- concentration is pH dependent but ka is not. The two reactions, activation and exchange, also differ in their activation energy bein 32 and 21.5 kcal/mol, respectively. It is concluded that, in the course of activation, Br- interacts at two distinct steps. First to produce a ternary, nonactive [enzyme-oxaloacetate-Br-] complex. From this complex, oxaloacetate dissociates and the oxaloacetate-free enzyme assumes its active form. Finally, the active enzyme is stabilized by binding another Br-. The rate-limiting step in deactivation is binding of oxaloacetate to active enzyme. The complex formed undergoes a very rapid transformation to the stable nonactive form. This pathway, under certain conditions, can reverse its direction and contribute to the overall rate of activation. It is suggested that the equilibrium between the two stable forms of the enzyme can be reached by two parallel pathways, each contributing independently to the observed rate of activation, while the final equilibrium is determined by the free energy between the products and the reactants.

Characterization of the component, which controls the transformation between the kinetic forms of the b cytochromes

1. In the presence of KCN and a saturating concentration of antimycin the reduction of the b-type cytochromes in submitochondrial particles is biphasic. This phenomenon was explained by suggesting the existence of two kinetic forms of cytochrome b:bA-the active form which was reduced in the rapid phase, and bS-the sluggish form which was reduced in the slow phase. The ratio between these forms and the transformation from one to other was controlled by the redox state of an unknown component, names "y", located between cytochromes b and c1. Pre-treatment with ascorbate plus N,N,N1,N1-tetramethyl-p-phenylenediamine transforms all the b-type cytochromes to their sluggish form, and the reduction by succinate follows slow monophasic kinetics. The name "dynamic control mechanism" was given to this mechanism [Eisenbach, M. & Gutman, M. (1975) Eur. J. Biochem. 52, 107-116] 2. Increasing concentrations of antimycin (0-2 nmol/mg) in the presence of KCN increased the fraction of the rapid phase of the reduction but did not affect the calculated absolute rates of the reduction. It is concluded that antimycin delays the reduction of "y" and thus permits the observation of the biphasic phenomen, but that it is not essential for the operation of this dynamic control mechanism.

The steady state activity of succinate dehydrogenase in the presence of opposing effectors.II. Reductive activation of succinate dehydrogenase in presence of oxaloacetate

The extent of the deactivation of the mitochondrial succinate dehydrogenase by oxaloacetate is a function of the redox state of the enzyme. Oxidized enzyme is deactivated by much lower concentrations of oxaloacetate than those needed to deactivate reduced enzyme. An accurate method for measuring this relationship is the redox titration of the enzymic activity of succinate dehydrogenase, carried out in the presence of oxaloacetate. For each concentration of oxaloacetate a different redox titration curve was reported with the apparent mid-potential decreasing with increasing oxaloacetate. These results are compatible with a model which proposes that both oxidized and reduced enzymes can form the catalytically non-active complex with oxaloacetate, but that the complex formed the the oxidized enzyme is more stable than that formed by the reduced enzyme. When the oxaloacetate concentration is low, reduction of the enzyme will lower the fraction of the succinate dehydrogenase-oxaloacetate complex, a reaction which we observe as reductive activation of the enzyme. If this experiment is repeated in the presence of high concentration of oxaloacetate, no activation of the enzyme takes place, but the low stability of the reduced enzyme oxaloacetate complex is revealed by the rapid exchange of the enzyme-bound oxaloacetate with the free ligand. The rate of this exchange is extremely slow at high positive potential and becomes faster upon lowering of the poise potential. The reductive activation of the succinate dehydrogenase is regarded as a two step reaction. In the first step the reduced non-active complex releases the oxaloacetate and in the second step the active form of the enzyme is evolved. These two steps can be observed experimentally; Reductive activation at a redox potential higher than the mid-potential of the oxaloacetate-malate couple (minus 166 mV) is characterized by Ea = 18 Kca/mole, the final equilibrium level of activation decreases upon lowering of the temperature. Reduction activation of the enzyme at minus 240 mV is a very rapid reaction which goes to completion at all temperatures tested and has an activation energy of 12.5 Kcal/mole. The mechanism of the reductive activation and its possible role in the regulation of succinate dehydrogenase in the mitochondria is discussed.

The steady state activity of succinate dehydrogenase in the presence of opposing effectors. 1. The effect of L malate and CoQH2 on the enzymic activity

Succinate dehydrogenase is subjected to positive and negative modulation. The negative modulators oxaloacetate and D- or L-malate transform the enzyme into a nonactive complex in which oxaloacetate is bound. The deactivation by malate involves its oxidation by the succinate dehydrogenase which then deactivates the enzyme. In the present study we measured the activity of succinate dehydrogenase in the presence of two opposing effectors,L-malate as deactivator and CoQH2 as an activator. With these opposingeffectors present, the catalytic activity of succinate dehydrogenase assumes a steady state, the level of which is a function of the concentration of the two effectors. At lowconcentration of L-malate all of the succinate dehydrogenase activity is protected by CoQH2, while at saturating malate concentrations only 60-70% of activity is protected. Kinetic analysis of the approach to the steady state indicates that the protective effect of CoQH2 is not due to its activator property but due to its ability ofreduce the enzyme. This was verified by carrying out a radox titration of succinatedehydrogenase activity in the presence of L-malate. A redox active component was characterized with E = +25 mV and n = 1.8. When this component is reduced, L-malate cannot deactivate the succinate dehydrogenase, but when in the oxidized state the enzyme is susceptible to such deactivation. It is proposed that this group participates in the regulation of the activity of succinate dehydrogenase in the mitochondria.

Dynamic control on the rate of the reduction of the b type cytochromes in submitochondrial particles

1. In the presence of antimycin and KCN the reduction of cytochrome b in phosphorylating submitochondrial particles followed a biphasic first-order kinetics. The transition from the first, rapid phase to the second, slow phase occurred while the reduction of chtochromes c + c1 and a through or around the antimycin block was still linear with time. Thus, the phase transition was due to a fall-off in the rate of cytochrome b reduction. 2. The biphasic reduction of cytochrome b was observed over a wide temperature range (0--30 degrees C), with succinate of NADH as electron donors and with phosphorylating particles or coupled rat-heart mitochondria. With rat-heart mitochondria the same biphasic reduction was observed in the presence of either carbonyl cyanide p-trifluoromethoxyphenylhydrazone or oligomycin. 3. In both the rapid and the slow phases, the rate of reduction of cytochrome b-561 was equal to that of b-565. Thus both cytochromes b-561 and b-565 were affected by the mechanism which determined the reduction-rate. Furthermore, each of these cytochromes could be reduced individually with rate constants typical of the slow phase. 4. The proportion of rapidly reduced to slowly reduced cytochrome b was independent of the degree of its reducibility and could be controlled by teh experimental conditions. When antimycin was used as the only inhibitor, 96% of the b-type cytochromes were reduced in the rapid phase. If the c and a-type cytochromes were first reduced by ascorbate and tetramethyl-p-phenylenediamine in the presence of KCN and antimycin, all the b-type cytochromes were fully reduced at the slow-rate. 5. With succinate, the rate of the rapid phase depended on the activation level of the succinic-dehydrogenase. The rate constant of the second phase was unaffected by the succinic dehydrogenase activity, if the preparation was more than 20% active. Furthermore, the rate constant of the slow reduction was the same with succinate, NADH, or even with durohydroquinone (which reacted directly with cytochromes b). 6. It is suggested that cytochrome b can exist in two forms: kinetically active or sluggish. The active form is rapidly reduced by the endogenous quinone (QH2) or durohydroquinone. The rate of the reduction of the active form by succinate or NADH is probably determined by the rate of the reduction of Q by the dehydrogenases. The second form of cytochrome b is characterized by its sluggish reduction by QH2 or durohydroquinone. 7. It is proposed that the transformation from the active to the sluggish form is induced by the reduction of a controlling group, named Y, located on the oxygen side of the antimycin inhibition site. When Y is oxidized, cytochrome b is in its active form, and when Y is reduced, cytochrome b is in its sluggish form. The nature of this kinetic control and a comparison with the mechanism controlling the reducibility of cytochrome b are discussed.