Potentiometric study of cytochrome c1aa3 from Thermus thermophilus

We have examined the redox behavior of the cytochrome c1aa3 complex from Thermus thermophilus. In potentiometric titrations the cytochrome c behaves as an independent center having n = 1 and E = 205 mV (NHE). Under the assumption that the individual centers equilibrate independently in this experiment, changes in the absorption band at 603 nm have been resolved into two components: cytochrome a (n = 1, Em = 270 mV, 60% spectral contribution) and cytochrome a3 (n = 2, Em = 360 mV, 40% spectral contribution). The n = 2 process was attributed to strong chemical coupling between cytochrome a3 and CuB. The enzyme was also titrated with a mixture of NADH and PMS, and the results are shown not to conform to a model of intramolecular equilibrium according to the equilibrium constants obtained from the potentiometric titration. It is suggested that a conformational equilibrium within the complex may control electron transfer between cytochromes a and a3.     

On periodic responses of a mathematical neuron model

The periodic responses of a mathematical neuron model, when periodically varying input stimuli are applied to the model, are investigated. An explicit representation of periodic responses is obtained. It is shown that a periodic response as a 0–1 string is a uniform string. That is, the 1's of the 0–1 string are distributed uniformly in the string.     

Characterization of a Mr = 56,000 polypeptide associated with 10S DNA polymerase alpha purified from calf thymus using monoclonal antibody.

Existence of a Mr = 56,000 polypeptide associated with 10S DNA polymerase alpha was shown by production of a monoclonal anti-calf thymus 10S DNA polymerase alpha antibody secreted from a hybridoma line named 3H1. The antibody bound three polypeptides with Mr = 180,000, 56,000 and 32,000 in hydroxylapatite fraction of 10S DNA polymerase alpha by immunoblot. The antibody co-precipitated the polypeptides with the large polypeptide (Mr = 150,000-140,000) of 10S DNA polymerase alpha with the aid of second antibody. Among three polypeptides, the Mr = 56,000 polypeptide was co-purified with DNA polymerase alpha through DNA-cellulose chromatography and repeated sucrose rate-zonal centrifugations. The Mr = 56,000 polypeptide was still associated with 10S DNA polymerase alpha after second sucrose rate-zonal centrifugation, but the amount of it was reduced. The polypeptide was banded at pH 7.2-8.0 and displayed microheterogeneity in respect of isoelectric point by isoelectrofocusing with 7 M urea, and showed weak DNA-binding property after blotting onto a nitrocellulose. The antibody against the polypeptide precipitated DNA polymerase alpha from human, rat, and mouse, and Mr = 56,000 and 32,000 polypeptides were detected in these DNA polymerase alpha fractions by immunoblot. These results suggest that the polypeptide with Mr = 56,000 may take part in the DNA polymerase reaction.     

Mg2+-dependent unwinding of DNA by nonhistone chromosomal protein HMG(1 + 2) from pig thymus as determined by DNA melting temperature analysis

In the previous studies with endonucleases specific for single-stranded DNA, we have indicated that the nonhistone chromosomal protein HMG(1 + 2) prepared from pig thymus has an activity to unwind DNA partially at low protein-to-DNA weight ratios (Yoshida, M. & Shimura, K. (1984) J. Biochem. 95, 117-124). In the present work, we have pursued the unwinding reaction by HMG(1 + 2) by thermal melting temperature analysis of DNA, and by investigating the effect of Mg2+ on the reaction. The melting temperature of DNA in the presence of HMG(1 + 2) at low protein weight ratios decreased in 2 mM Tris-HCl, pH 7.8, whereas it increased at higher ratios. The depressions of melting temperature by HMG(1 + 2) at low ratios were not observed either in the system of 2 mM Tris-HCl, pH 7.8, containing EDTA or in the system containing samples treated in advance with EDTA. An addition of Mg2+ to the system reproduced the depression of melting temperature at low protein-to-DNA ratios as well as the increase at higher ratios. Analysis by Mg2+-equilibrated gel filtration revealed that HMG(1 + 2) is a Mg2+-binding protein. However, the depression of melting temperature at low protein-to-DNA ratios was not due to removal of Mg2+ from DNA by HMG(1 + 2). From these results, it is concluded that HMG(1 + 2) causes a partial DNA unwinding detectable by thermal melting temperature analysis of DNA, and that Mg2+ is necessary for the unwinding reaction.     

Stereospecific incorporation of hydrogens from NADPH in elongation of very long fatty acyl-CoA by swine cerebral microsomes

The elongation of arachidoyl-CoA by swine cerebral microsomes resulted in the production of behenic acid (22:0) and lignoceric acid (24:0) concomitantly. When 4S-[4-²H₁]NADPH was used for the elongation of arachidoyl-CoA, the incorporation of two deuterium atoms into 22:0 was observed by the technique of mass fragmentography. Furthermore, the incorporation of four deuterium atoms into 24:0 was also detected. On the other hand, when 4R-[4-²H₁]NADPH was used, no deuterium was incorporated into the elongated products.     

Interaction between 2-chloroadenosine and alpha-adrenoceptors in rat vas deferens

The effect of 2-chloroadenosine (2CA) on the binding of alpha 1- and alpha 2-adrenoceptor ligands in the rat vas deferens was investigated. In homogenates of vas deferens, 2CA (10(5)M) increased 3H-clonidine maximal binding sites from an undetectable level to 0.71 +/- 0.08 pmol/g. wet weight or 10.1 +/- 1.1 fmol/mg protein (N=12). This effect lasted for at least 5 hours after removal of 2CA. Concurrent addition of 1.25 mM theophylline completely abolished the effect of 2CA. A similar effect of 2CA on 3H-clonidine binding was observed following incubation of intact tissues with 2CA prior to homogenization. The effect of 2CA were similar in potency in the homogenate to that in the intact organ, suggesting that 2CA-sensitive sites are located on the outer surface of the plasma membrane. The binding of 3H-prazosin was not influenced by the presence of 10(-5)M 2CA. Contractions of isolated vasa deferentia induced by norepinephrine and phenylephrine were not changed by 10(-5)M 2CA, but the inhibition by clonidine of contractions induced by electric stimulation was enhanced by preincubation for 30 min with 10(-5)M 2CA. The results suggest that 2CA increases the number of available alpha 2-adrenoceptors and this interactions occurs, at least in part, presynaptically.     

Differences in Ca2+ mobilization induced by alpha-adrenergic agonist and phosphatidic acid in cultured hepatocytes

In an attempt to elucidate the relationship between phosphatidylinositol breakdown and alpha-adrenergic responses, effects of phosphatidic acid and phosphatidylinositol related metabolites on Ca²⁺ mobilization and glucose output in cultured hepatocytes were examined. Norepinephrine induced the net ⁴⁵Ca²⁺ efflux from preloaded cells and stimulated glucose output via alpha-adrenergic receptor stimulation, whereas phosphatidic acid caused ⁴⁵Ca²⁺ uptake to cells and did not stimulate glucose output. Myo-inositol-monophosphate, diglyceride and arachidonic acid, which are released by phosphatidylinositol breakdown, had no effect on ⁴⁵Ca²⁺ efflux and glucose output in cells. These results suggest that phosphatidic acid and phosphatidylinositol related metabolites can not mimic the alpha-adrenergic actions in cultured hepatocytes.     

Lipoprotein lipase-like activity in the liver of mice with Sarcoma 180

The triglyceride lipase (TGL) activity of liver homogenates of mice with Sarcoma 180 was measured. The liver homogenate of normal or tumor-bearing mice was treated with 0.25% Triton X-100 and centrifuged at 100,000 g for 60 min, and the supernatant was applied to a heparin-Sepharose column. In normal mice, most of the TGL activities in the supernatant was eluted with 0.75 M NaCl from the column. In mice with Sarcoma 180, the TGL gave two peaks on heparin-Sepharose column chromatography, which were eluted with 0.75 M and 1.5 M NaCl, respectively. The activity in the first peak (0.75 M NaCl eluate) decreased; that in the second peak (1.5 M NaCl eluate) increased, and the ratio of the second peak to the first peak increased during tumor development. The livers of normal mice and mice on day 10 after tumor inoculation were perfused with heparin. The highest rate of the TGL release occurred within 1 min of heparin perfusion, and the bulk of heparin-releasable activity appeared within 2 min of perfusion in both normal and tumor-bearing mice. The TGL activity in liver perfusate of tumor-bearing mice, as well as that of liver homogenate, was resolved on a heparin-Sepharose column into two peaks, which were eluted with 0.75 M and 1.5 M NaCl, and most of the activity was eluted with 1.5 M NaCl. The nature of the TGL activity eluted from a heparin-Sepharose column was investigated. In both liver homogenates and liver perfusates, the first peak did not require serum for maximal activity and was relatively resistant to a high concentration of NaCl or protamine sulfate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Protective antibodies in human sera against encapsulated strains of Staphylococcus epidermidis

Passive protective antibodies in 100 samples of normal human sera against challenge with three representative capsular type strains of Staphylococcus epidermidis in mice were examined. Six of them passively protected mice against capsular type I; 17 protected against capsular type II; one against capsular type III; and one against both capsular types I and II. The activities were sensitive to 2-mercaptoethanol and were absorbed out either with rabbit anti-human IgG serum, rabbit anti-human IgA serum or rabbit anti-human IgM serum. Also, the sera activities absorbed out with cell surface polysaccharide extracted from three representative capsular type strains. These results indicate that the protective activities were specifically related to three major immunoglobulins against the above cell surface polysaccharides.