Correlation of intrinsic fluorescence and conformation of smooth muscle myosin

The addition of ATP to turkey gizzard myosin causes an enhancement of the intrinsic tryptophan fluorescence. The level of fluorescence enhancement is determined by the myosin conformation. The transition of myosin from the folded (10 S) state to the extended (6 S) state is accompanied by a decrease in the fluorescence level. Phosphorylation-dephosphorylation of myosin does not directly influence fluorescence and will induce changes only if the myosin conformation is altered. Under the appropriate conditions, phosphorylation of myosin favors the transition of 10 S to 6 S. The phosphorylation dependence of the associated fluorescence decrease is not linear, and it is proposed that the phosphorylation of both light chains is required for the full transition. The tryptophan residues involved respond to the binding of ATP at the hydrolytic sites. Since the fluorescence properties of gizzard myosin are influenced by the myosin conformation, it is reasonable to assume that the active sites are also modified by the shape of the myosin molecule.     

Sources of fish in the ephemeral western iishana region of the Cuvelai–Etosha Basin in Angola and Namibia

The triangle between the Kavango and Kunene rivers is drained by the Cuvelai, an ephemeral and deltaic drainage system covering more than 100 000 km². In good rainfall years, the area becomes populated by fish communities dominated by five species migrating southward towards the endorheic Etosha Pan, the basin’s terminal sump. When water dries up, fish subsequently die-off and their sudden appearance in rainy years has captivated scientists for decades. The current study was prompted by hitherto untapped indigenous knowledge through narratives of opportunistic fish harvesting of migrating fish at temporary connections between the Kunene River and the Cuvelai- Etosha Basin. A reconnaissance fish survey in 2017 was complemented by digital satellite images and elevation data analyses. Results support the presence of at least three major ephemeral fish migration routes. The dominant fish genera migrating upstream in Kunene tributaries comprise Enteromius, Oreochromis and Clarias, all eurytopic and known to undertake upstream, lateral and downstream migrations on floodplains. Although other notable fish refugia in the Cuvelai–Etosha Basin are yet to be identified, there is a necessity for the protection and management of these migration routes in tandem with studies on the nature and extent of this inter-basin fish migration under climate change and variability.     

Compensatory renal growth in human fetuses with unilateral renal agenesis

To determine whether compensatory growth of the kidney occurs during fetal life we studied 20 human specimens with a unilateral kidney as an isolated defect. The mean combined kidney weight to body weight ratio x 100 in controls was 0.76 +/- 0.14 (SD) and in the solitary kidney cases (after doubling the kidney weight) was 1.26 +/- 0.35 (SD). This significant increase leads us to hypothesize that the increased weight may be due to an induced negative feedback system involving a renotropic factor. From histologic studies a uniform increase in all nephron elements was found. Why should a fetus with adequate placental clearance of metabolic wastes need increased renal size?     

The saxitoxin receptor of the sodium channel from rat brain. Evidence for two nonidentical beta subunits

The saxitoxin receptor of the sodium channel purified from rat bran contains three types of subunits: alpha with Mr approximately 270,000, beta 1 with Mr approximately 39,000, and beta 2 with Mr approximately 37,000. These are the only polypeptides which quantitatively co-migrate with the purified saxitoxin receptor during velocity sedimentation through sucrose gradients. beta 1 and beta 2 are often poorly resolved by gel electrophoresis in sodium dodecyl sulfate (SDS), but analysis of the effect of beta-mercaptoethanol on the migration is covalently attached to the alpha subunit by disulfide bonds while the beta 1 subunit is not. The alpha and beta subunits of the sodium channel were covalently labeled in situ in synaptosomes using a photoreactive derivative of scorpion toxin. Treatment of SDS-solubilized synaptosomes with beta-mercaptoethanol decreases the apparent molecular weight of the alpha subunit band without change in the amount of 125I-labeled scorpion toxin associated with either the alpha or beta subunit bands. These results indicate that the alpha and beta 1 subunits are labeled by scorpion toxin whereas beta 1 is not and that the beta 2 subunit is covalently attached to alpha by disulfide bonds in situ as well as in purified preparations.     

The molecular organization of the beta-globin complex of the deer mouse, Peromyscus maniculatus

Recombinant DNA clones have been isolated that contain 80 kb of the beta-globin complex from the deer mouse, Peromyscus maniculatus. Comparisons of this complex with that from the laboratory mouse, Mus domesticus (with an order 5'-Hbby, Hbb-bhO, Hbb-bhl, Hbb-bh2, Hbb-bh3, Hbb-bl, Hbb-b2 3') highlight organizational trends in the beta-globin complex since the two species diverged. Unlike other mammals studied thus far, the deer mouse possesses three adult genes. Partial sequence analysis indicates that each of the three adult genes is intact and hence may be functional. Hybridization of one of the two Mus pseudogenes, Hbb-bh3, to genomic blots from Peromyscus reveals that it has a homologous counterpart in Peromyscus. Homologous genes to the two gamma-like Mus genes, Hbb-bhO and Hbb-bhl, are also found in Peromyscus. The strong hybridization between the Hbb-bhl genes and significant nucleotide similarity between the Hbb-bhO genes suggest that both pairs are important for the ontogeny of these mice although no known product has been identified for the Hbb-bhO genes. The presence of Hbb-bhO and Hbb-bhl in Peromyscus suggests that the duplication that created this related gene set occurred before the two lineages diverged. A single gene for Hbb-y has been isolated from Peromyscus. The adult region in Peromyscus has undergone significant divergence from the same region in Mus, having three rather than two adult genes, the acquisition of at least 15 kb of extra DNA relative to Mus, and possibly the loss of the Hbb-bh2 pseudogene. The nonadult region of the complex, in contrast, contains the same set of genes apparently distributed over the same amount of DNA as in the Mus beta- globin complex. This observation suggests that the embryonic region of the complex is more evolutionarily stable than the adult region.