Stephen W. Schaffer

Taurine enhancement of calcium binding to rat heart sarcolemma.

The effect of taurine on calcium binding to isolated rat heart sarcolemmal membrane was examined. Taurine was observed to increase calcium binding to the low affinity sites in both high sodium-low potassium and low sodium-high potassium buffers. Taurine was also seen to antagonize the inhibition of calcium binding to the sarcolemma caused by both verapamil and lanthanum. Nevertheless, membrane structural changes due to taurine could not be detected using the spin label ESR probe 2N14. A possible regulatory role of taurine is discussed.

The identification of taurine receptors from rat heart sarcolemma

Two sets of taurine receptors on rat heart sarcolemma have been identified. The high affinity taurine receptors (Kd=3.5×10−4M) show a non-cooperative binding profile while the low affinity taurine receptors exhibit positive cooperativity. Taurine binding to the membrane exhibits a typical bell shaped pH profile with maximum binding occurring at pH 8.0. The maximum temperature for binding is 24°C. The effect of various taurine analogues on the receptors was investigated. It was found that binding is prevented by hypotaurine and inhibited to a lesser degree by isethionic acid and cysteine sulfinic acid, while β-alanine was found to increase taurine binding. The effect of several hydrolytic enzymes was also examined and it was shown that several proteases and phospholipase C inhibit binding. The results indicate that the taurine receptors are membrane bound proteins in a phospholipid environment.

Dissociation of cAMP changes and myocardial contractility in taurine perfused rat heart

Abstract It has been determined that the inotropic effects of taurine in the rat heart are not necessarily mediated through changes in cyclic nucleotide levels. Taurine caused a transient 2-fold decrease in cAMP levels, and this was accompanied by a slight (5%), but significant positive inotropic effect. This cannot be explained by an antagonism of cAMP levels by 3′, 5′ -guanosine monophosphate (cGMP), since the latter remained essentially unchanged. Epinephrine, as is known, caused a rapid increase in cAMP levels. Perfusion with both taurine and epinephrine increased cAMP levels to the same extent as perfusion with epinephrine alone.

Solubilization and characterization of cardiac sarcolemmal taurine-binding proteins

Abstract Cardiac sarcolemma preparations of both pig and rat ventricles were found to possess two sets of taurine-binding components. The two proteins from pig heart were solubilized with the detergent Ammonyx-Lo. Characterization of these solubilized proteins revealed that both components are glycoproteins and retain the binding properties observed for the membrane isolate. However, the characterization also revealed several differences between the proteins including their binding specificities, their affinities for taurine, their binding isotherms, and their molecular sizes. Possible functions of these two taurine-binding proteins are discussed.

Mathematical analysis of carbon dioxide transport by blood

Abstract A theoretical study is presented of acid-base balance on the microcirculation level, and of the interactions that occur between the various phenomena influencing this balance. This involves the study of carbon-dioxide transport by blood and its relationship to oxygen transport, as well as a study of the buffer systems that are intimately connected to the transport of these gases. A mathematical model of carbon dioxide transport in the microcirculation is constructed that includes the physiological and biochemical processes important to CO2 transport and acid-base balance. Using perturbation techniques, methods of analysis of the governing equations are developed in order to obtain analytic solutions under a broad range of physiological conditions. The analysis presented forms the basis for the study of more complex physiological problems, such as transient following an occlusion.

Use of 5'-UTP-agarose for ribonuclease affinity chromatography.

Abstract The use of commercially available 5′-UTP-agarose as an affinity chromatography resin for RNase has been described. It was shown that at pH 5.3, 0.025 m piperazine-HCl buffer was effective for the adsorption of active RNase A and exhibited little nonbiospecific binding as has been shown earlier for SepharoseaPhpUp [Stewart, G. R., and Stevenson, K. J. (1973) Biochem. J. 135 , 427–441]. Phosphate buffer at either pH 3.0 or 5.45 eluted essentially all of the RNase activity added to the column; however, pH 5.45 was slightly more efficient. Competitive elution experiments with 2′(3′)-UMP yielded a linear plot of 1 (V − V o vs [I]. From this plot K I and K IM were calculated to be 70 and 130 μ m , respectively. It is suggested that since this material is different from that which is used most often for RNase A affinity chromatography, it may prove useful for RNase binding studies.

Cardiac taurine levels and sarcolemmal calcium binding activity in furazolidone-induced cardiomyopathy.

Abstract 1. Cardiac taurine levels and sarcolemmal calcium binding activity were investigated in control turkey poults and in poults with furazolidone (FZ)-induced cardiomyopathy. 2. FZ at a dose of 700 ppm added to the feed of poults from 2 to 5 weeks post-hatching significantly reduced cardiac taurine levels and elevated the sarcolemmal calcium bindingactivity at high calcium levels. 3. The effect of FZ on cardiac taurine levels was reversed by removing the drug from the diet for a period of 2 weeks. 4. Data suggests that the cardiotoxicity of FZ is associated with severe damage to the sarcolemma.

Selective reduction of seminal ribonuclease by glutathione.

Abstract Incubation of seminal ribonuclease with glutathione leads to the formation of a monomeric species which exhibits twice the specific activity of the native dimer. The monomer was found to possess two mixed disulfides of glutathione at residues 31 and 32, the residues ordinarily involved in the intermolecular disulfide bonds linking the subunits of the native dimer. Formation of the monomer results in only minor changes in the far ultraviolet circular dichroism spectra. The rate of the glutathione-facilitated dissociation reaction is fairly slow, requiring 60 min for completion. Attempts to dimerize the monomer all failed, implying that the dissociation reaction is irreversible. The glutathione reduced monomer was compared with the monomer formed during the regeneration of reduced, denatured bovine seminal ribonuclease in the presence of glutathione. By all criteria examined, the two monomeric forms are identical. It is concluded that the mixed disulfide monomer is the favored form of the enzyme in the presence of glutathione.

Regeneration of reduced-denatured seminal ribonuclease: effect of modification at cysteines 31 and 32.

Abstract The temperature dependences of glutathione-facilitated regeneration of ribonuclease A and seminal ribonuclease are quite different although the two proteins are homologous. This difference in the two enzymes appears to result from the presence of two additional half-cystine residues in seminal ribonuclease. When these two cysteines are alkylated with either a neutral or positively charged blocking agent, the regeneration process becomes seemingly temperature insensitive. On the other hand, negatively charged agents are less effective in restoring normal regeneration kinetics. The modifications also render the protein more stable against thermal inactivation, a process which presumably contributes to the unusual temperature dependence of regeneration. These data reveal the potential importance of peripheral groups in the regeneration and stability of proteins. A model is proposed to explain these observations.