Effect of adenosine deaminase inhibitors on Fcμ receptor expression in human T-cell cultures

Incubation of human peripheral blood T-lymphocyte cultures with 100 μM EHNA or 1 μM pentostatin results in the delayed appearance of Fcμ, receptor-bearing cells. The percentage of Tμ-positive cells approaches control levels by 24–30 hr despite the lack of detectable adenosine deaminase activity. Tγ to Tμ transition was more effectively inhibited than To to Tμ in studies with the individual subpopulations. The inhibitory effect of pentostatin or EHNA on the appearance of Fcμ receptor-positive cells was reversible with exogenous undine or 2′-deoxycytidine. These results indicate that pyrimidine deprivation affects the appearance of Fcμ receptors in T-cell cultures, and that despite the continued inhibition of ADA the effect on Fcμ is reversible by 24 hr without the addition of exogenous pyrimidines.     

The action of tributyltin chloride on the uptake of proline and glutamine by intact cells of Escherichia coli.

Tributyltin chloride inhibits growth and uptake of glutamine and proline into intact cells of Escherichia coli. It causes efflux of the accumulated amino acids. A pH gradient generated in intact cells and everted membrane vesicles is dissipated by this compound. These effects do not require lipoic acid but are dependent on the presence of chloride, bromide, or iodide ions. We conclude that tributyltin chloride can catalyse a transmembrane OH- -anion exchange exchange reaction and that this is its mode of inhibition of the uptake of these amino acids. The response of proline and glutamine uptake to the inhibitor is similar and is consistent with the transport of both amino acids requiring an electrochemical gradient of protons.     

B chromosome variation in Euphydryas colon (Lepidoptera: Nymphalidae)

Cytogenetic analysis of an Idaho population of the checkerspot butterfly, Euphydryas colon, has revealed considerable inter- and intra-individual variation in chromosome number which turns out to be a classic case of B chromosome variation. The basic chromosome complement of the species is n (, )=31. The A chromosomes were aligned equatorially at mitotic metaphase and metaphase II, and axially at metaphase I, indicating a restriction of centric activity at the first meiotic division. No failure of pairing between homologous A chromosomes was observed and, although a marked asynchrony of chromatid separation was found to be characteristic of mitotic telophase and telophase II, the frequency of macrospermatid formation was low. The B chromosomes were at least partly heterochromatic but exhibited some variation in both pycnosity and size. Mitotically stable B-containing individuals showed a preponderance of unpaired Bs at first metaphase and these divided at either first or second anaphase. The presence of Bs was associated with a heightened production of abnormal spermatids particularly in individuals with high numbers of B chromosomes. Among the 25 individuals sampled, 21 carried from 1–6 B chromosomes, and of these 14 were mitotically stable. In all 7 unstable individuals the mean number of B chromosomes per cell exceeded the modal number. Assuming that the modal number represents the zygotic number, these results suggest that a mechanism to boost the number of B chromosomes exists in males of E. colon.     

Enhanced stability of the Na+-dependent amino acid-transport system after lymphocyte activation.

Two cytochromes b with absorption maxima at 555 and 562 nm and differing in their mid-point redox potentials are synthesized in Pseudomonas AM1 during growth on methanol or succinate in batch culture, or in NH4+-limited or carbon-limited continuous culture. Both cytochromes b were also present in a cytochrome c-deficient mutant in all growth conditions.     

Isozymal differention between two species of Prosopis

The patterns of five multilocus isozyme systems were investigated in seed, shoot and cotyledon tissue of two species of mesquite, Prosopis glandulosa var. glandulosa and P. pallida. The isozymes of malate dehydrogenase, peroxidase, esterase, alcohol dehydrogenase and acid phosphatase from each of these tissues were analysed by starch gel electrophoresis and specific histochemical stains. In the case of each enzyme system examined, there were distinctly different isozymes which could be utilized to differentiate between these two species.     

Lack of involvement of lipoic acid in membrane-associated energy transduction in Escherichia coli.

Oxidative phosphorylation, active transport of proline, aerobic- and ATP-driven proton translocation and transhydrogenation of NADP⁺ by NADH, occurred in lipoic acid-deficient cells or vesicles of a lipoic acid auxotroph of $\text{E. coli}$, W1485 lip 2. Addition of lipoic acid had little effect on these processes. Tributyltin chloride, which has been proposed to inhibit oxidative phosphorylation by reaction with lipoic acid (Cain $\text{et al.}$, Biochem. J. (1977) $\text{166}$, 593), was an effective inhibitor of aerobic and ATP-dependent proton translocation and transhydrogenation in lipoic acid-deficient vesicles from this organism. Our results do not support the proposal of Partis $\text{et al.}$ (FEBS Lett. (1977) $\text{75}$, 47) that lipoic acid is involved in the energy transducing processes associated with the membrane of $\text{E. coli}$.     

Calcium-binding properties of cardiac and skeletal troponin C as determined by circular dichroism and ultraviolet difference spectroscopy.

Calcium titration of the conformational change in cardiac and skeletal troponin C (TN-C) was followed by circular dichroism (CD) at pH values in the range from 5.2 to 7.4. Computer analysis was used to resolve the contributions from the different classes of Ca2+ -binding sites. At pH 6.94 in skeletal TN-C, apparent affinity constants for calcium of 1.8 x 10(7) and 4.5 x 10(5) M-1 were determined for the two classes of binding sites. The more sophisticated computer analysis of the data has revealed a substantial CD contribution from the low-affinity sites (approximately 30% of the high affinity contribution at pH 6.94) and suggests that skeletal TN-C with Ca2+ bound at the low-affinity sites is in a different conformation from that when just the high-affinity sites are occupied, in agreement with a recent nuclear magnetic resonance (NMR) study on this system (Seaman, K. B., Hartshorne, D. J. & Bothener-By, A. A. (1977) Biochemistry 16,4039-4046). With the cardiac protein at pH 7.07, an apparent affinity constant for calcium of 2.0 x 10(7) M-1 was calculated while no low-affinity site at this pH was detected by CD. On the other hand, at lower pH values, such as 6.05, a CD contribution from the cardiac low-affinity Ca2+ -binding site is detected with an apparent binding constant of 3.7 +/- 0.7 x 10(4) M-1. At the lower pH values, protonation of a class of carboxyl groups in each protein which possesses a high pKa (6.2-6.3) elicits the conformational change at the high-affinity sites with a corresponding decrease in the overall magnitude of the Ca2+ -evoked changes. The expression of a conformational change upon Ca2+ binding at the level of the low-affinity sites is enchanced by protonation of a class of carboxyls with a pKa of 6.3 in cardiac TN-C and 6.7-6.8 with the skeletal homologue. In both cases, this contribution is reduced upon protonation of carboxyls with pKa less than or equal to 5.5. It was also observed that the low-affinity sites of skeletal TN-C have a much larger role to play in the total conformational change than the low-affinity sites of cardiac TN-C, a finding probably related to the inability of site 1 in the cardiac protein to bind calcium. In the cardiac protein, the Ca2+ -induced tyrosine difference-spectrum maximum is reduced from deltaepsilonM,287nm =330M-1.cm-1 to 20M-1.cm-1 by protonation of a class of groups with a pKa of 6.4, presumably the same carboxyl groups as those invoved in the CD conformational contribution from the high-affinity binding sites. No such effect was observed for the skeletal protein where deltaepsilonM,287nm was constant at 110M-1 .cm-1 over the pH range studied. The dramatic alterations in the tyrosine environment of cardiac TN-C with pH are attributed to either or both of the tyrosines located in the two high-affinity Ca2+ -binding sites (sites 3 and 4)...