Biochemical and morphological characterization of a plasma membrane-enriched fraction from bovine parathyroid cells

A fraction of enriched plasma membranes from bovine parathyroid cells has been prepared by differential centrifugation. Biochemical characterization shows that this fraction has a specific activity enrichment of 7.2-fold in ouabain-sensitive Na+-K+ ATPase, and 3.5-fold in 5'-nucleotidase. Less than 4% of the total mitochondria and lysosomes are present within the plasma membranes, while microsomal contamination accounts for 14% of total specific activity. Parathyroid hormone radioimmunoassay also reveals the presence of some secretory granules within the plasma membrane fraction. The characteristic morphological aspect of the unusual surface membrane is shown by freeze-fracture electron microscopy. In the enriched pellets, vesicles identified as having a plasma membrane origin have variable sizes, and 50% show an inside-out conformation. Even though the plasma membrane fraction described herein is not absolutely free from contamination by other subcellular components, this protocol represents the first attempt to purify surface membrane from parathyroid tissue and provide the starting material for understanding, at a molecular level, the properties of extracellular Ca2+ regulation and its coupling with secretion of parathyroid hormone.     

Modification of rat liver iodothyronine 5'-deiodinase activity with diethylpyrocarbonate and rose bengal; evidence for an active site histidine residue

Iodothyronine 5'-deiodinase activity of rat liver microsomes was rapidly and completely lost by treatment with diethylpyrocarbonate (DEP) and by photo-oxidation with Rose Bengal (RB). In both cases inactivation followed pseudo first order reaction kinetics. Inactivation by DEP was diminished in the presence of substrate or competitive inhibitors, and was reversed by hydroxylamine treatment. In addition to photo-oxidation, deiodinase activity was also inhibited by RB in the dark. This inhibition was reversible and competitive with substrate (Ki 60 nM). These results suggest the location of an essential histidine residue at or near the active site of rat liver iodothyronine deiodinase.     

Molecular heterogeneity of canine cholecystokinin in portal and peripheral plasma

The release of molecular forms of cholecystokinin (CCK) into the portal and peripheral blood in response to an intraduodenal perfusion of sodium oleate (9 mmol X h-1) was studied in six conscious dogs with chronic portal vein catheters. Immunoreactive CCK as concentrated from 20 ml plasma by C18 SEP PAK cartridges and the pattern of molecular forms of CCK were studied by G50 gel filtration. CCK-like immunoreactivity (CCK-LI) was measured in the column eluates with antibody 5135, which measures gastrin and CCK equally and requires the intact carboxyl-terminus for full recognition. Gastrin was measured specifically with antibody 1611. Intraduodenal perfusion with oleate did not alter basal gastrin release. Release of CCK-LI by intraduodenal oleate was calculated by the increments of the integrated CCK-LI peaks over basal. Total CCK-like immunoreactivity (CCK-LI), calculated by integration of all CCK-LI peaks in gel filtration eluates, increased over basal by 12 fmol/ml in the portal and by 6 fmol/ml in the peripheral plasma after intraduodenal perfusion with sodium oleate. The main molecular forms eluted on gel filtration in positions of CCK33,39 and of CCK8. The pattern of CCK in the peripheral plasma was similar to that in the portal plasma except that in the peripheral plasma large molecular forms were more abundant than small forms. This finding was confirmed when CCK39 and CCK8 were infused either into the portal vein or into the peripheral vein and peripheral plasma CCK levels were measured. Elimination of CCK8 after portal vein infusion compared to peripheral vein infusion was about 3 times higher than that of CCK39. The abundance of large molecular forms of CCK in the circulating blood which are similar in potency to small forms, underlines their role in the physiology of CCK.     

Assessment of a model for intron RNA secondary structure relevant to RNA self-splicing--a review

A widespread class of introns is characterized by a particular RNA secondary structure, based upon four conserved nucleotide sequences. Among such "class I" introns are found the majority of introns in fungal mitochondrial genes and the self-splicing intron of the large ribosomal RNA of several species of Tetrahymena. A model of the RNA secondary structure, which must underlie the self-splicing activity, is here evaluated in the light of data on 16 further introns. The main body or "core structure" of the intron always consists of the base-paired regions P3 to P9 with the associated single-stranded loops, with P2 present also in most cases. Two minority sub-classes of core structure occur, one of which is typical of introns in fungal ribosomal RNA. Introns in which the core structure is close to the 5' splice site all have an internal guide sequence (IGS) which can pair with exon sequences adjacent to the 5' and 3' splice sites to align them precisely, as proposed by Davies et al. [Nature 300 (1982) 719-724]. In these cases, the internal guide model allows us to predict correctly the exact location of splice sites. All other introns probably use other mechanisms of alignment. This analysis provides strong support for the RNA splicing model which we have developed.     

Glucose-6-phosphate dehydrogenase porbandar: A new slow variant with slightly reduced activity in a South African family of Indian descent

A new variant of the red cell enzyme glucose-6-phosphate dehydrogenase has been detected in a South African male of Indian descent and in several of his relatives. The enzyme variant is characterized by slow electrophoretic mobility, low Michaelis constants for the substrates glucose-6-phosphate and NADP, and increased utilization of the substrate analogues 2-deoxyglucose-6-phosphate and deamino-NADP relative to the normal (B⁺) enzyme. There is no evidence that the enzyme variant, for which the name G6PD Porbandar is suggested, is associated with any hematological abnormality.The Atomic Energy Board and the South African Medical Research Council provided support for part of this work.     

Physiological and biochemical changes associated with cotton fibre development. II. Auxin oxidising system

Changes in IAA oxidase, and in cytoplasmic and ionically wall-bound peroxidase activities were studied in the developing fibres of three cotton cultivars ( Gossypium hirsutum L. cv. Gujarat-67, cv. Khandwa-2 and G. herbaceum L. cv. Digvijay), designated as long, medium and short staple cultivars, respectively. In all the three cultivars IAA oxidase activity was low during the fibre elongation phase, while the activity increased significantly during the secondary thickening phase. The increase in IAA oxidase activity in the three cultivars showed close correspondence with their respective total period of elongation. No relationship between cytoplasmic peroxidase activity and fibre development was discernible. The ionically bound wall peroxidase activity, however, recorded low levels during the elongation phase and higher levels during the secondary thickening phase. The role of wall peroxidase in cessation of elongation growth is discussed.     

Stimulation of gastrin secretion from the perfused rat stomach by somatostatin antiserum

The effect of a high capacity somatostatin antiserum on antral gastrin secretion was examined in an isolated vascularly perfused rat stomach preparation. Infusion of somatostatin antiserum diluted 1:1 and 1:9 with Krebs buffer solution produced significant increases in gastrin secretion throughout the period of infusion. Neither infusion of somatostatin antiserum diluted 1:99 nor infusion of control rabbit serum had any effect on gastrin secretion. The data indicate that antral somatostatin excercises a continous restraint on gastrin secretion in the basal state.     

Distributional patterns and an additional species of thePassiflora vitifolia complex: Amazonian species diversity due to edaphically differentiated communities

Field studies in Amazonian Peru show that thePassiflora vitifolia complex, a microcosm of many larger taxa, is concentrated in Amazonia with 4 ecologically separated species. One species is restricted to seasonally inundated forests, a second to non-inundated white sand soils, a third to non-inundated lateritic soils, and the fourth mostly to non-inundated alluvial soils. A new combination is formally proposed to recognize the white sand taxon, previously regarded as a variety, as a distinct species:P. involucrata. The importance of -diversity in maintaining high Amazonian species diversity is emphasized.     

Habitat segregation in a salt marsh among adult sticklebacks (Gasterosteidae)

Synopsis The spatial distribution, seasonal abundance and diel activity of four sticklebacks,Gasterosteus aculeatus, G. wheatlandi, Pungitius pungitius, andApeltes quadracus. coexisting in a St. Lawrence salt marsh were examined to see how these closely related species share their habitat. While all four species breed in the Riviè des Vases, a tidal creek, only three species are found in the adjacent salt marsh pools,A. quadracus being absent. Results are interpreted in terms of avoidance of interspecific competition for space during the relatively short breeding season at this latitude.