Purification of lipoamide dehydrogenase from Ascaris muscle mitochondria and its relationship to NADH:NAD+ transhydrogenase activity

Lipoamide dehydrogenase (NADH:lipoamide oxidoreductase EC 1.6.4.3) has been isolated from Ascaris suum muscle mitochondria. This activity has been purified to apparent homogeneity from both the pyruvate dehydrogenase complex and from 150,000g mitochondrial supernatants which were devoid of pyruvate dehydrogenase complex activity. The enzymes from both sources exhibited similar kinetic, catalytic, and regulatory properties and appear to be identical as judged by polyacrylamide gel electrophoresis. The native enzyme acts as a dimer, containing 2 mol of FAD, and has a subunit molecular weight of 54,000, as estimated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel chromatography. The enzyme also possesses substantial NADH:NAD⁺ transhydrogenase activity. Heat denaturation and differential solubilization experiments imply that the transhydrogenase activity previously reported is, in fact, associated with the lipoamide dehydrogenase moiety of the Ascaris pyruvate dehydrogenase complex. Whether or not this activity functions physiologically in hydride ion translocation, as previously suggested, remains to be demonstrated.     

Fluence response relationship of carotenogenesis inNeurospora crassa

The fluence response of the blue light induced carotenoid synthesis inNeurospora is biphasic. Using fluence rates between 0.3 and 40 Wm^-2, increasing illumination times beyond 16 min (at 20°C) result in a second rise of the amount of carotenoids synthesized in the subsequent dark period. On altering the temperature, the transition point to the second phase of the response is shifted to shorter/longer illumination periods with increasing/decreasing temperature, respectively. The transition point can also be shifted by administering high fluence rates of near UV light: The start of the second phase is already triggered after an irradiation time of 2 min. The findings suggest that elements of the transduction sequence become depleted and senstivity recovers in a temperature-dependent process. The biphasic response and the effects of UV light are discussed in relation to the transduction mechanism and to the ecological significance.Presented in part at the meeting of the Deutsche Botanische Gesellschaft, September 1978, Marburg, Federal Republic of Germany     

Oxygen inhibition of photosynthesis in the C4 species Amaranthus graecizans L.

In the C₄ plant, Amaranthus graecizans, increasing [O₂] from 2% up to 100% inhibited photosynthesis, quantum yield, and the carboxylation efficiency, and increased the CO₂ compensation point () from 2 to about 12 l/l. The O₂ inhibition of photosynthesis was fully reversible. When changing from 2.5 to 40% O₂ and vice versa, about 1 h was required for full equilibration with an O₂ inhibition of 18%; whereas in wheat, a C₃ species, inhibition of photosynthesis and its reversal occurs within minutes after changing [O₂], resulting in 63% inhibition of photosynthesis by 45% O₂. These differences in O₂ inhibition between a C₄ and C₃ species can be explained by high diffusive resistance across bundle-sheath cells of C₄ plants and the increased CO₂/O₂ ratio in bundle-sheath cells which is the consequence of the C₄ cycle. In A. graecizans, increased with increasing [O₂] but tended to reach a maximum at relatively high O₂ levels. The lack of a linear increase in as previously observed for C₃ species indicates that a considerable amount of photorespired CO₂ may be re-fixed with increasing levels of O₂. In comparison to previous reports with other C₄ species, photosynthesis of A. graecizans shows greater sensitivity to O₂, with a noticeable inhibition occurring with shifts from 2 to 21% O₂. A. graecizans has characteristics of other C₄ species with respect to Kranz anatomy, localization of PEP carboxylase in mesophyll cells and RuBP carboxylase in bundle-sheath cells, and little fractionation among carbon isotopes during CO₂ fixation. The basis for the higher sensitivity of photosynthesis of A. graecizans to O₂ may be based upon a lower diffusive resistance of gases across bundle-sheath cells than in some other C₄ species.Abbreviations CE carboxylation efficiency - RuBP ribulose-1,5-bisphosphate - CO₂ compensation point     

Spiral growth in the radially-expanding piloboloid mutants ofPhycomyces blakesleeanus

The growth zone of the sporangiophore of a piloboloid mutant,pil, ofPhycomyces expands radially at an increased rate until the growth zone becomes nearly spherical, in sharp contrast to that of the wild-type sporangiophore which exhibits longitudinal elongation only and is conical. The rotation of thepil sporangiophore reverses its direction from clockwise (CW) to counterclockwise (CCW) during the period of increased radial expansion, and the CCW rotation continues as long as does the radial expansion. The direction of rotation and the time of reversal are correlated with the relative rates of cell-wall expansion in the longitudinal and transverse directions. The CCW rotation of the sporangiophore of this mutant can be explained by the behavior of the microfibrils, as previously proposed to explain the rotation of the wild-type sporangiophore.Abbreviations CW clockwise - CCW counterclockwise — both as viewed from above     

Progestin metabolism in the rhesus monkey corpus luteum

For the purpose of describing the pathway by which estrogens are synthesized in the rhesus monkey ($\text{Macaca}$$\text{mulatta}$) corpus luteum (CL), CL were obtained during the midluteal phase of the menstrual cycle and fragments incubated with equimolar amounts of [7-³H]pregnenolone plus [4-¹⁴C]progesterone. Metabolites including ³H-progesterone, ³H, ¹⁴C-20α-dihydroprogesterone, ³H, ¹⁴C-17-hydroxyprogesterone, ³H-estrone and ³H-estradiol-17β appeared in the medium during the first 20 minutes of incubation, ³H, ¹⁴C-Androstenedione was not consistently noted until after 60 minutes. Despite the fact that the ¹⁴C/³H-17-hydroxyprogesterone ratio quickly approached a constant value in the medium, ¹⁴C-estrogens were not detected in the medium or tissue fragments suggesting that progesterone was not a principal precursor for estrogen synthesis. As evidenced by the observation that the ¹⁴C/³H-progesterone ratio was significantly higher in luteal fragments than the 17-hydroxyprogesterone ratio, 17-hydroxyprogesterone appeared to be synthesized from pregnenolone both by way of progesterone and by another route which did not include progesterone. C₂₁- and C₁₈-Steroids were more concentrated in tissue fragments after 120 minutes of incubation than in the medium indicating that these steroids were sequestered by luteal tissue.     

The effect of positive assortative mating at one locus on a second linked locus

Summary Considerations proceed from a model of positive assortative mating based on genotype at one locus, with an arbitrary number of alleles, assuming no selection, mutation, or migration, hypothetically infinite population size, and discrete non-overlapping generations. From these conditions, inferences are made about the genotypic structure at a linked locus, as well as about the corresponding 2-locus gametic structure.The following main results are presented: in the course of the generations, the genotypic structure at the second locus and the 2-locus gametic structure always tend to a limit responsive to the initial conditions concerning the joint genotypic structure at the two loci and the degree of assortativity and linkage. A complete, analytical representation of the limits is given. In particular, if assortative mating is only partial and at the same time linkage is not complete, a population is not able to maintain a permanent deviation of the gametic structure from linkage equilibrium, and thus the genotypic structure at the second locus tends to Hardy-Weinberg proportions. On the other hand, if initial linkage disequilibrium is combined with partial assortative mating and complete linkage (or with complete assortative mating and unlinked loci) the population maintains this disequilibrium and thus the genotypic structure at the second locus need not tend to Hardy-Weinberg proportions. It turns out that the conditions not only of complete linkage, but also of unlinked loci together with complete assortativity, imply no change in gametic structure from the initial structure.In order to demonstrate the influence of several parameters on the speed of convergence to and the magnitude of the respective limits, several graphs are included.     

Paramagnetic probes in NMR and EPR studies of membrane enzymes

The applications of paramagnetic probes to problems of structure and mechanism are discussed from the point of view of the membrane enzymologist. Problems unique to membrane systems are discussed, and a variety of nuclear and paramagnetic probes are evaluated. Three membrane ATPase (kidney (Na+ + K+)-ATPase, Ca2+-ATPase from sarcoplasmic reticulum and Mg2+-ATPase from kidney) are used to describe the types of experiments which can be done, the information which can be obtained and the limitations involved. Nuclear relaxation studies employing 1H, 7Li+, 31P and 205Tl+ nuclei are described. The advantages and disadvantages of Mn2+, Gd3+ and Cr3+ as paramagnetic probes are discussed in terms of the three ATPases. The theory and interpretation of Mn2+ and Gd3+ EPR spectra are evaluated in studies with the (Na+ + K+)-ATPase and Ca2+-ATPase, respectively.     

A spectroscopic study of metal ion and ligand binding to β-lactamase II

β-Lactamase II has two metal-binding sites. The electronic spectra of Cd(II)- and Co(II)-substituted β-lactamase II have been investigated. It is suggested that a thiol ligand is involved in metal binding at the first site. The stoichiometric dissociation constants for Co(II) binding to β-lactamase II were estimated to be 0.13 and 2.66 mM (pH 6.0, 4°C, 1 M NaCl) by equilibrium dialysis. Competition between Zn(II) and Co(II) for the first metal binding site suggests a value of 0.7 μM (pH 6.0, 30°C, 1 M NaCl) for the dissociation constant o Zn(II).The electronic spectra of the Co(II) enzyme lead to the suggestion that the coordination geometries around the metal ions in the first and second sites are related to those of a distorted tetrahedron and octahedron, respectively.