Biomedical subjects
Publications and source records attributed to A A Benson.
Fortuitous preparation and experiences led to the opportunity to use radioactive carbon dioxides to discern the path of carbon in photosynthesis. The search for the CO2 acceptor led to recognition of the growth stimulatory effect of methanol and its derivatives. With the techniques developed, radiochromatographic exploration led to discovery of major membrane lipids containing phosphorus, sulfur, and arsenic.
Using (13)C-NMR, we demonstrate that [(13)C]methanol readily entered sycamore (Acer pseudoplatanus L.) cells to be slowly metabolized to [3-(13)C]serine, [(13)CH(3)]methionine, and [(13)CH(3)]phosphatidylcholine. We conclude that the assimilation of [(13)C]methanol occurs through the formation of (13)CH(3)H(4)Pte-glutamate (Glu)(n) and S-adenosyl-methionine, because feeding plant cells with [3-(13)CH(3)]serine, the direct precursor of (13)CH(2)H(4)Pte-Glu(n), can perfectly mimic [(13)CH(3)]methanol for folate-mediated single-carbon metabolism. On the other hand, the metabolism of [(13)C]methanol in plant cells revealed assimilation of label into a new cellular product that was identified as [(13)CH(3)]methyl-beta-D-glucopyranoside. The de novo synthesis of methyl-beta-D-glucopyranoside induced by methanol did not require the formation of (13)CH(3)H(4)Pte-Glu(n) and was very likely catalyzed by a "transglycosylation" process.
Three isoforms of calcitonin (CT) exist in salmonids. Isohormones I and II are expressed in the pink salmon Oncorhynchus gorbuscha. We report here the existence in this species of a CT gene and of its transcripts, which encode for a fourth isohormone, the salmon CT (sCT) IV. This new CT gene was identified by PCR from genomic DNA and by sequencing the amplified DNA. The expression of this CT gene was established in ultimobranchial body and brain, by reverse transcription-PCR, hybridization and sequencing. The sCT IV gene, like the sCT I gene, is a complex transcription unit, containing exons encoding for a CT as a calcitonin gene-related peptide (CGRP) molecule. The predicted peptide, sCT IV, has a greater homology with the eel CT and the sCT II than with the sCT I. Alignment of the sCT IV with other fish and chicken CT showed amino acid modifications in similar positions as those found during evolution. The predicted salmon CGRP IV peptide is highly homologous to the known CGRP molecules in other species, confirming the high conservation of the molecule during evolution. This identification of a new salmon CT gene is interesting both for the therapeutic potential represented by the new molecules encoded by this gene and for phylogenetic studies.
Calcitonin is an important physiological regulator of salmon gills. Although the calcitonin receptor was found in salmon gills, the critical question concerning the source of the hormone remained unanswered. In this communication, evidence is presented for expression of calcitonin mRNA and its encoded peptide in gills of the pink salmon, Oncorhynchus gorbuscha. The expression of calcitonin gene transcripts was demonstrated by reverse transcription-polymerase chain reaction, Southern hybridization, and sequencing. The sequencing identified a sequence corresponding to that of exon 4 of the salmon calcitonin gene. Expression of the encoded calcitonin gene in gills was detected by radioimmunoassay in gill extracts. This synthesis of calcitonin in gills, which also possess specific receptors to the peptide, suggests function of an autocrine or paracrine process producing calcitonin in this tissue. These observations confirm and extend previous reports on the physiological role of calcitonin in fish gills.
Foliar sprays of aqueous 10-50% methanol increased growth and development of C3 crop plants in arid environments. The effects of low levels (< 1 ml per plant) of methanol were observed for weeks after the brief time necessary for its rapid metabolism. Within several hours, foliar treatment with methanol resulted in increased turgidity. Plants treated with nutrient-supplemented methanol showed up to 100% increases in yields when maintained under direct sunlight in desert agriculture. In the shade and when winter crops were treated with methanol, plants showed no improvement of growth. When repeatedly treated with nutrient-supplemented methanol, shaded plants showed symptoms of toxicity. Repeated methanol treatments with glycine caused increased turgidity and stimulated plant growth without injury under indirect sunlight, but indoors with artificial illumination, foliar damage developed after 48 hr. Addition of glycerophosphate to glycine/methanol solutions allowed treatment of artificially illuminated plants indoors without injury. Plants with C4 metabolism showed no increase in productivity by methanol treatment. Plants given many applications of aqueous methanol showed symptoms of nutrient deficiency. Supplementation with a source of nitrogen sustained growth, eliminating symptoms of deficiency. Adjustment of carbon/nitrogen ratios was undertaken in the field by decreasing the source of nitrogen in the final application, resulting in early maturation; concomitantly, irrigation requirements were reduced.
The gill phospholipids of 2 Pacific salmon species, Oncorhynchus keta and O gorbuscha, were composed of 38-43% phosphatidylcholine (PC) and 19-22% phosphatidylethanolamine (PE). Ether phosphoglycerides constituted 4-8% of the total PC fraction and 37-51% of the PE fraction. No significant changes in gill phospholipids were observed between those of pre-spawning fish in sea water and those of spawned salmon in the river. Cholesterol, however, was higher in the latter (0.59% vs 0.38%).
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Lipids constituted 0.6-2.2% wet wt of the gills of 11 species of aquatic animals (4 bivalves, a crustacean and 6 fishes). Phospholipids, largely phosphatidylcholine (PC) and phosphatidylethanolamine (PE), are major components of all species. The plasmalogen contents of these lipids were 47-291 mumol/g, with the highest values found for bivalve gill total lipids and the catfish phospholipid fraction.
The effect of calcitonin (CT) and parathyroid hormone (PTH) on carbonic anhydrase (carbonate hydrolyase, EC 4.2.1.1.) activity was tested in human erythrocyte hemolysates and with purified carbonic anhydrases I and II. The most important effect was on carbonic anhydrase II: CT showed a 2-fold increase and PTH showed a 50% decrease of carbonic anhydrase activity. This effect was observed at low hormonal concentrations and suggests the importance of CT in regulating carbonic anhydrase activity in the two important sites of CO2 exchange, erythrocyte and lung.
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Arsenic concentrates in the kidneys of the giant clams of Australia's Great Barrier Reef. The highest concentrations measured were 1004 parts per million, of which most, 2066 parts per million, were in the water-soluble fraction containing trimethylarsoniumlactate and its derivatives. This accumulation is ascribed to a mechanism in which oceanic arsenate is assimilated by symbiotic zooxanthellae and subsequently deposited in host tissues. The gills are the major site of arsenic excretion by these animals. Gill membrane arsenolipids mediate exposure of their trimethylarsonium groups to the sea and its biological oxidative activities.
The binding of salmon calcitonin was investigated in subcellular fractions obtained from normal porcine lung. Only the membrane fraction (density, 1.14 g/cm3) showed specific binding for calcitonin. Specific binding of 125I-labeled salmon calcitonin was competitively inhibited by concentrations of unlabeled homologous hormone in the range 0.01-1 nM. Half-maximal inhibition of binding was observed with 0.12 nM salmon calcitonin. Scatchard analysis of the data suggested the presence of one class of binding sites with a mean affinity constant of 0.9 X 10(10) M-1 and a mean receptor number of 40 X 10(8)/mg of protein. The binding of salmon calcitonin was highly specific; half-maximal inhibition of binding was observed with 63.8 nM bovine calcitonin, the hormone corticotropin having no effect in this system.
Isolated salmon gills, under simulated in vivo conditions, transported calcium ion into the ambient seawater when perfused with Ringer's solution containing salmon calcitonin. Similar enhancement of phosphate efflux was observed. Calcitonin caused simultaneous decreases in perfusate flow rates. The effects act synergistically to diminish net plasma calcium concentrations.
Leopard shark triacylglycerol lipase has been characterized as a crude pancreatic preparation. The enzyme demonstrated an absolute requirement for trihydroxy bile salts for activity with natural bile salts of the shark giving a 4-fold greater stimulation of activity than pure sodium taurocholate. Bile salts also protected the enzyme from apparent inactivation by p-chloromercuribenzoate and trypsin treatment. The shark lipase demonstrated a temperature optimum of 36 degrees C and was rapidly inactivated at 50 degrees C even in the presence of bile salts. Divalent metal ions were required for activity with Ca2+ providing the greatest stimulation. At 22 degrees C, pH 8.5 and in the presence of natural bile salts, the apparent V was about 0.6 mumol fatty acid released/min per mg protein. The shark enzyme hydrolyzed over 90% of the fatty acids from trioleovylglycerol and methyl esters of pancreatic lipase-resistant fatty acids were hydrolyzed at the same rate as typical fatty acid methyl esters. Hydrolysis of triacylglycerol proceeded about ten-times faster than wax ester hydrolysis. The kinetic properties of the leopard shark enzyme were compared to other bile salt-dependent lipolytic enzymes. Pancreatic lipase activity was not detected.
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