The Reactions of the Isolated α and β Chains of Human Hemoglobin with Oxygen and Carbon Monoxide

Abstract The values of the equilibrium and kinetic constants for the reactions with oxygen and carbon monoxide of the isolated α and β chains of human hemoglobin, both in the form with sulfhydryl groups blocked by p-hydroxymercuribenzoate and in the form with freely titratable sulfhydryl groups, have been determined. The data show clearly that the behavior of the isolated chains is not only unlike that of hemoglobin A, but also differs markedly from that of myoglobin. Since the isolated chains behave as simple systems without heme-heme interaction (n = 1 in the O2 equilibrium), they have been used to test the proposition that the binding of a ligand is correctly expressed as a single step reaction. In at least one case it appears that it is not

Seasonal Dynamics and Defoliation Impact on Herbage Yield in Aspen Boreal Habitats of Alberta

Within the aspen boreal ecosystems, little information exists on the seasonal dynamics of available herbage and the effects of varying defoliation regimes on accumulated herbage growth and associated opportunities for animal production. We examined seasonal changes in herbage phytomass in conjunction with defoliation treatments in Bromus inermis-Poa pratensis grasslands in central Alberta. Changes in herbage pools were examined by sampling at five monthly intervals from April to September 1997 and 1998, inclusive. Vegetation was also subjected to a factorial experiment with an initial defoliation in late-May, June or July, at heights of 2.5, 7.5, or 15 cm, and repeated at 3-, 6- or 9-week intervals until the end of September. Green herbage, standing dead and fallen litter increased from spring to summer and decreased from summer to fall. Average growing conditions resulted in a peak phytomass of 350 g m-2, and varied by year. Weathering losses of green herbage, standing dead and fallen litter over winter were 34%, 52% and 51%, respectively. Dry matter losses of total herbage (all three pools) over winter were 58% of 1997 summer green phytomass. Initial timing, height, and frequency of clipping all affected accumulated herbage yield (P < 0.001). The greatest accumulated herbage yield was from clipping initiated in May. Light clipping resulted in less phytomass accumulation relative to moderate and heavy clipping. Clipping frequencies of six and nine weeks resulted in similar phytomass removal, but were greater than herbage removal associated with three weeks frequency. The interaction between clipping date and frequency of clipping demonstrates the importance of temporal rest and sensitivity of forage plants to defoliation, and lends support to the use of rotational grazing systems

The Rates of Combination of the Isolated Chains of Human Hemoglobin with Oxygen

Abstract The rates of combination of the isolated chains of human hemoglobin with oxygen have been measured by flash photolysis and stopped flow methods. The two experimental methods give similar results, and furthermore the data compare well with those obtained recently by the temperature jump relaxation method. The measured association rates are compared with the values predicted from the previously measured equilibrium and dissociation rate constants. A significant discrepancy is noted in the case of the β chains. In addition, the rates of replacement of oxygen by carbon monoxide as functions of the relative ligand concentrations have been measured, and the observed dependences are compared to those predicted from the equilibrium and kinetic constants for the individual liganding reactions

Structure and Oxygen Affinity of Crystalline des-His-146β Human Hemoglobin in the T State *

To correlate directly structure with function, the oxygen affinity and the three-dimensional structure of crystals of the T quaternary state of des-His-146beta human hemoglobin have been determined by polarized absorption microspectrophotometry and x-ray diffraction crystallography. In des-His-146beta, the COOH-terminal histidine residues of the beta chains of hemoglobin A have been removed. Oxygen binding to crystalline des-His hemoglobin is non-cooperative and independent of pH. The oxygen affinity is 1.7-fold greater than that of the crystalline state of hemoglobin A. Removal of His-146beta results in a small movement of the truncated COOH-terminal peptide and in a very small change in quaternary structure. Previously, similar studies on T state crystals of des-Arg-141alpha hemoglobin showed that removal of the COOH termini of the alpha chains results in much larger effects on oxygen affinity and on quaternary structure. Kinetic studies in solution reveal that at pH 7.0, the rates of CO combination with deoxygenated des-His-146beta in the absence and presence of inositol hexaphosphate are 2.5- and 1.3-fold, respectively, more rapid than for hemoglobin A. The values for des-Arg are 7.6- and 3.9-fold. The properties of the T state of hemoglobin both in the crystal and in solution are influenced to a greater degree by the interactions associated with Arg-141alpha than those associated with His-146beta

Mevalonate-Farnesal Biosynthesis in Ticks: Comparative Synganglion Transcriptomics and a New Perspective

Juvenile hormone (JH) controls the growth, development, metamorphosis, and reproduction of insects. For many years, the general assumption has been that JH regulates tick and other acarine development and reproduction the same as in insects. Although researchers have not been able to find the common insect JHs in hard and soft tick species and JH applications appear to have no effect on tick development, it is difficult to prove the negative or to determine whether precursors to JH are made in ticks. The tick synganglion contains regions which are homologous to the corpora allata, the biosynthetic source for JH in insects. Next-gen sequencing of the tick synganglion transcriptome was conducted separately in adults of the American dog tick, Dermacentor variabilis, the deer tick, Ixodes scapularis, and the relapsing fever tick, Ornithodoros turicata as a new approach to determine whether ticks can make JH or a JH precursor. All of the enzymes that make up the mevalonate pathway from acetyl-CoA to farnesyl diphosphate (acetoacetyl-CoA thiolase, HMG-S, HMG-R, mevalonate kinase, phosphomevalonate kinase, diphosphomevalonate decarboxylase, and farnesyl diphosphate synthase) were found in at least one of the ticks studied but most were found in all three species. Sequence analysis of the last enzyme in the mevalonate pathway, farnesyl diphosphate synthase, demonstrated conservation of the seven prenyltransferase regions and the aspartate rich motifs within those regions typical of this enzyme. In the JH branch from farnesyl diphosphate to JH III, we found a putative farnesol oxidase used for the conversion of farnesol to farnesal in the synganglion transcriptome of I. scapularis and D. variabilis. Methyltransferases (MTs) that add a methyl group to farnesoic acid to make methyl farnesoate were present in all of the ticks studied with similarities as high as 36% at the amino acid level to insect JH acid methyltransferase (JHAMT). However, when the tick MTs were compared to the known insect JHAMTs from several insect species at the amino acid level, the former lacked the farnesoic acid binding motif typical in insects. The P450s shown in insects to add the C10,11 epoxide to methyl farnesoate, are in the CYP15 family; this family was absent in our tick transcriptomes and in the I. scapularis genome, the only tick genome available. These data suggest that ticks do not synthesize JH III but have the mevalonate pathway and may produce a JH III precursor

Mary Clifford Webster Darling Correspondence

Entries include some correct biographical information typed by the Maine State Library and handwritten correspondence on a Fredericka Manor card and plain paper stationery

Planning Considerations Related to Collecting and Analyzing Samples of the Martian Soils

The Mars Sample Return (MSR) End-to-End International Science Analysis Group (E2E-iSAG [1]) established scientific objectives associ-ated with Mars returned-sample science that require the return and investigation of one or more soil samples. Soil is defined here as loose, unconsolidated materials with no implication for the presence or absence of or-ganic components. The proposed Mars 2020 (M-2020) rover is likely to collect and cache soil in addition to rock samples [2], which could be followed by future sample retrieval and return missions. Here we discuss key scientific consid-erations for sampling and caching soil samples on the proposed M-2020 rover, as well as the state in which samples would need to be preserved when received by analysts on Earth. We are seeking feedback on these draft plans as input to mission requirement formulation. A related planning exercise on rocks is reported in an accompanying abstract [3]

Roles of key active-site residues in flavocytochrome P450 BM3

Abbreviations used: P450, cytochrome P450 mono-oxygenase; ImC12, 12-(imidazolyl)dodecanoic acid; 1-PIM, 1-phenylimidazole.The effects of mutation of key active-site residues (Arg-47, Tyr-51, Phe-42 and Phe-87) in Bacillus megaterium flavocytochrome P450 BM3 were investigated. Kinetic studies on the oxidation of laurate and arachidonate showed that the side chain of Arg-47 contributes more significantly to stabilization of the fatty acid carboxylate than does that of Tyr-51 (kinetic parameters for oxidation of laurate: R47A mutant, Km 859 µM, kcat 3960 min-1; Y51F mutant, Km 432 µM, kcat 6140 min-1; wild-type, Km 288 µM, kcat 5140 min-1). A slightly increased kcat for the Y51F-catalysed oxidation of laurate is probably due to decreased activation energy (DG‡) resulting from a smaller DG of substrate binding. The side chain of Phe-42 acts as a phenyl 'cap' over the mouth of the substrate-binding channel. With mutant F42A, Km is massively increased and kcat is decreased for oxidation of both laurate (Km 2.08 mM, kcat 2450 min-1) and arachidonate (Km 34.9 µM, kcat 14620 min-1; compared with values of 4.7 µM and 17100 min-1 respectively for wild-type). Amino acid Phe-87 is critical for efficient catalysis. Mutants F87G and F87Y not only exhibit increased Km and decreased kcat values for fatty acid oxidation, but also undergo an irreversible conversion process from a 'fast' to a 'slow' rate of substrate turnover [for F87G (F87Y)-catalysed laurate oxidation: kcat 'fast', 760 (1620) min-1; kcat 'slow', 48.0 (44.6) min-1; kconv (rate of conversion from fast to slow form), 4.9 (23.8) min-1]. All mutants showed less than 10% uncoupling of NADPH oxidation from fatty acid oxidation. The rate of FMN-to-haem electron transfer was shown to become rate-limiting in all mutants analysed. For wild-type P450 BM3, the rate of FMN-to-haem electron transfer (8340 min-1) is twice the steady-state rate of oxidation (4100 min-1), indicating that other steps contribute to rate limitation. Active-site structures of the mutants were probed with the inhibitors 12-(imidazolyl)dodecanoic acid and 1-phenylimidazole. Mutant F87G binds 1-phenylimidazole > 10-fold more tightly than does the wild-type, whereas mutant Y51F binds the haem-co-ordinating fatty acid analogue 12-(imidazolyl)dodecanoic acid > 30-fold more tightly than wild-type

Thinking like a man? The cultures of science

Culture includes science and science includes culture, but conflicts between the two traditions persist, often seen as clashes between interpretation and knowledge. One way of highlighting this false polarity has been to explore the gendered symbolism of science. Feminism has contributed to science studies and the critical interrogation of knowledge, aware that practical knowledge and scientific understanding have never been synonymous. Persisting notions of an underlying unity to scientific endeavour have often impeded rather than fostered the useful application of knowledge. This has been particularly evident in the recent rise of molecular biology, with its delusory dream of the total conquest of disease. It is equally prominent in evolutionary psychology, with its renewed attempts to depict the fundamental basis of sex differences. Wars over science have continued to intensify over the last decade, even as our knowledge of the political, economic and ideological significance of science funding and research has become ever more apparent