Search

Arising from Kai, F. M., Tyler, S. C., Randerson, J. T. & Blake, D. R. 476, 194-197 (2011)To understand the reasons for global CH4 changes since the 1990s, Kai et al. evaluated a combined record of observed tropospheric CH4 mole fractions as well as ?13C-CH4 and ?D-CH4 measurements from mid latitudes of both hemispheres. Their data set shows a strongly decreasing inter-hemispheric difference (IHD) in ?13C-CH4 from ?0.24 ± 0.11‰ during 1989-1993 to ?0.10 ± 0.04‰ during 2001-2005, which they largely attribute to decreasing rice emissions during the last two decades. Here we show that the experimental data used by Kai et al. are probably biased because the authors used only one continental mountain station (Niwot Ridge, Colorado, USA) as representative of the entire Northern Hemisphere, thereby incorrectly determining the IHD of ?13C-CH4. Our more comprehensive data set-representing background air in both hemispheres-shows that the IHD of ?13C-CH4 has changed by less than 0.05‰ since 1990; the conclusion drawn by Kai et al. of a significant reduction of NH microbial sources is, thus, not constrained by our data. [ABSTRACT FROM AUTHOR]

Alpha atrial natriuretic peptide (alpha-ANP) and brain natriuretic peptide are homologous polypeptide hormones involved in the regulation of fluid and electrolyte homeostasis. These two natriuretic peptides apparently share common receptors and stimulate the intracellular production of cyclic GMP as a second messenger. Molecular cloning has defined two types of natriuretic peptide receptors: the ANP-C receptor of relative molecular mass (Mr) 60-70,000 (60-70 K), which is not coupled to cGMP production and may function in the clearance of ANP and the ANP-A receptor of Mr 120-140 K, which is a membrane form of guanylate cyclase in which ligand binding to the extracellular domain activates the cytoplasmic domain of the enzyme. Here we report the cloning and expression of a second human natriuretic peptide-receptor guanylate cyclase, the ANP-B receptor. The ANP-B receptor is preferentially activated by porcine brain natriuretic peptide rather than human alpha-ANP, whereas the ANP-A receptor responds similarly to both natriuretic peptides. These observations may have important implications for our understanding of the central and peripheral control of cardiovascular homeostasis.

The role of complementary hydrogen bonding as a determinant of biological specificity has been examined by protein engineering of the tyrosyl-tRNA synthetase. Deletion of a side chain between enzyme and substrate to leave an unpaired, uncharged hydrogen-bond donor or acceptor weakens binding energy by only 0.5-1.5 kcal mol-1. But the presence of an unpaired and charged donor or acceptor weakens binding by a further approximately 3 kcal mol-1.

Guanylate cyclase has been strongly implicated as a cell-surface receptor on spermatozoa for a chemotactic peptide, and on various other cells as a receptor for atrial natriuretic peptides. Resact (Cys-Val-Thr-Gly-Ala-Pro-Gly-Cys-Val-Gly-Gly-Gly-Arg-Leu-NH2), the chemotactic peptide released by sea urchin Arbacia punctulata eggs, is specifically crosslinked to A. punctulata spermatozoan guanylate cyclase. After the binding of the peptide the state of guanylate cyclase phosphorylation modulates enzyme activity. We report here that the deduced amino-acid sequence of the spermatozoan membrane form of guanylate cyclase predicts an intrinsic membrane protein of 986 amino acids with an amino-terminal signal sequence. A single transmembrane domain separates the protein into putative extracellular and cytoplasmic-catalytic domains. The cytoplasmic carboxyl-terminal 95 amino acids contain 20% serine, the likely regulatory sites for phosphorylation. Unexpectedly, the enzyme is homologous to the protein kinase family.

Atrial natriuretic peptide (ANP) is a polypeptide hormone whose effects include the induction of diuresis, natriuresis and vasorelaxation. One of the earliest events following binding of ANP to receptors on target cells is an increase in cyclic GMP concentration, indicating that this nucleotide might act as a mediator of the physiological effects of the hormone. Guanylate cyclase exists in at least two different molecular forms: a soluble haem-containing enzyme consisting of two subunits and a non-haem-containing transmembrane protein having a single subunit. It is the membrane form of guanylate cyclase that is activated following binding of ANP to target cells. We report here the isolation, sequence and expression of a complementary DNA clone encoding the membrane form of guanylate cyclase from rat brain. Transfection of this cDNA into cultured mammalian cells results in expression of guanylate cyclase activity and ANP-binding activity. The ANP receptor/guanylate cyclase represents a new class of mammalian cell-surface receptors which contain an extracellular ligand-binding domain and an intracellular guanylate cyclase catalytic domain.