Auxin controls Golgi-localized glucan synthetase activity in the maize mesocotyl

Decapitation or red light irradiation (R) inhibited growth and Golgi-localized glucan synthetase (GS I) activity in the mesocotyl of intact maize (Zea mays L.) seedlings. Applied auxin (indole-3-acetic acid) prevented the effects of R and of decapitation on both growth and GS I. Auxin applied several hours after irradiation prevented any further decline in GS I but did not restore it. Mesocotyl segments incubated in solution elongated in response to auxin but lost GS I with time regardless of the presence of exogenous auxin. An attached seed was necessary for maintenance of GS I in the dark-grown mesocotyl.Abbreviations GS glucan synthetase - IAA indole-3-acetic acid - R red light     

The Role of Chloride in Acetylcholine Metabolism

Abstract: The chloride dependence of acetylcholine (ACh) synthesis and release and of choline uptake was studied in synaptosomal preparations from rat brain. The substitution of propionate for chloride, in the presence of 35 m m -potassium, lowered the ACh content of the synaptosomes. However, in the presence of 5 m m -potassium, the ACh level in synaptosomes was reduced, but significantly less so. Propionate had no effect on choline acetyltransferase (EC 2.3.1.6) activity when measured in a standard chloride-containing medium. In the presence of propionate, the spontaneous release of ACh was unchanged, but potassium-stimulated release of ACh was markedly reduced as compared with a chloride-containing medium. The synthesis of ACh, as measured by the net increase in the amount of ACh in the synaptosomes and that released to the medium, was reduced with propionate at 5 m m -potassium and was totally inhibited when the potassium concentration was increased to 35 m m . Choline uptake studies revealed that with propionate only a low-affinity component of the choline transport system existed. Further, the V _max was markedly reduced when the potassium concentration was increased to 35 m m . The results suggest that under certain conditions choline transported by a low-affinity system might provide a substantial source of choline for ACh synthesis.     

Synthesis of phosphatidylcholine under possible primitive Earth conditions

Summary Using a primitive Earth evaporating pond model, the synthesis of phosphatidylcholine was accomplished when a reaction mixture of choline chloride and disodium phosphatidate, in the presence of cyanamide and traccs of acid, was evaporated and heated at temperatures ranging from 25° to 100°C for 7 hours. Optimum yields of about 15% were obtained at 80°C. Phosphatidylcholine was identified by chromatographic, chemical and enzymatic degradation methods. On enzymatic hydrolysis with phospholipase A₂ and phospholipase C, lysophosphatidylcholine and phosphorylcholine were formed, respectively. Alkaline hydrolysis gave glycerophosphorylcholine. The synthesis of phosphatidylcholine as the major compound was accompanied by the formation of lysophosphatidylcholine in smaller amounts. Cyanamide was found to be essential for the formation of phosphatidylcholine, and only traces of HCl, of the order of that required to convert the disodium phosphatidate to free phosphatidic acid were found necessary for the synthesis. This work suggests that phosphatidylcholine, which is an essential component of most biological membranes, could have been synthesized on the primitive Earth.     

Effect of α-Methylphenylalanine and Phenylalanine on Brain Polyribosomes and Protein Synthesis

Abstract: A chronic hyperphenylalanemia was effectively produced in developing mice by daily administrations of phenylalanine (2 mg/g body wt) and a phenylalanine hydroxylase inhibitor α-methyl-D, L-phenylalanine (0.43 mg/g body wt). The presence of α-methylphenylalanine in newborn mice inhibited 65–70% of hepatic phenylalanine hydroxylase activity within 12 h. Since this maximum inhibition persisted for 24 h or longer, decreased enzyme activity was maintained by daily administrations. Whereas concentrations of phenylalanine increased approximately 40-fold in both plasma and brain following injection of α-methylphenylalanine and phenylalanine, plasma levels of tyrosine were not altered significantly. Concomitant with changes in phenylalanine concentrations we observed the brain polyribosomes' disaggregation, which reached a maximum 3 h after injection and persisted as long as 18 h. Polyribosomes did not become refractory to as many as 10 daily injections of α-methylphenylalanine and phenylalanine. In addition to polyribosome disaggregation, chronic hyperphenylalanemia reduced the rates of polypeptide chain elongation on polyribosomes isolated from brain homogenates.     

Phenylcoumarins from Ochrocarpus Siamensis

Two new phenylcoumarins, 6-butyryl-5-hydroxy-4-phenylseselin and 6-butyryl-5,7-dihydroxy-8-(3,3dimethylallyl)-4-phenyleoumarin, were isolated from the flowers of Ochrocarpus siamensis.     

Clays in prebiological chemistry

Summary In this review an attempt is made to highlight the structures and properties of clay that may contribute to a better understanding of the role of clays in chemical evolution. The adsorption of organic molecules on clays has been demonstrated, as has the synthesis of bioorganic monomers in the presence of clays. For instance, amino acids (glycine, aspartic acid, threonine, alanine and others) as well as purines and pyrimidines, have been obtained from CO and NH₃ in the presence of clays at relatively high temperatures (250-325°C). Carbohydrates are also easily derived from formaldehyde at relatively low temperatures (80°C). The oligomerization of biochemical monomers, mediated by clays has also been shown to result in the formation of polymer molecules basic to life. For instance the condensation of amino acyl adenylates at room temperature in the presence of montmorillonite is known to yield polypeptides in discrete ranges of molecular weights with degrees of polymerization up to 56. Clays have also been found to affect the condensation of mononucleotides to oligonucleotides. Although the role of clays in the origin of metabolic pathways has not been demonstrated, it is possible that clays may have played a cooperative role with catalytic peptides in an intermediate stage of prebiological chemistry preceding the emergence of life on this planet.     

Regulation of Muscarinic Receptor-Mediated Cyclic GMP Synthesis by Cultured Mouse Neuroblastoma Cells

Mouse neuroblastoma clone N1E-115 has muscarinic acetylcholine receptors that mediate cyclic GMP synthesis. This receptor-mediated response is not significantly higher than background until the cells have been maintained in the stationary phase for at least 1 week. The basis of the influence of time in culture on the cyclic GMP response was investigated. The relative amount of cyclic GMP synthesized by intact cells was measured by radioactively labeling the GTP pool with [³H]guanine, incubating cells with agonists, and then chromatographically isolating [³H]cyclic GMP. Carbamylcholine-, ionophore X-537A-, and sodium azide-induced cyclic GMP formation increased with time in culture to a maximum of 13-, 9-, and 2.5-fold above basal, respectively. There was no change in the number or the apparent affinity of the muscarinic receptors as measured by [³H]quinuclidinyl benzylate ([³H]QNB) binding. In addition, there was no change in the apparent affinity of the receptors for agonist as measured by the ability of carbamylcholine to displace the specific binding of [³H]QNB. Guanylate cyclase activity per milligram protein and per cell in-creased six- and sevenfold, respectively, from day 0 to day 22. However, this increase in guanylate cyclase appeared to precede the marked increase in sensitivity of the cells to agonists. These data suggest that, in addition to guanylate cyclase and muscarinic receptors, there is another factor which is responsible for the development of this muscarinic receptor-mediated response.     

Sucrose:sucrose fructosyltransferase and fructan:fructan fructosyltransferase from allium cepa

Sucrose: sucrose fructosyltransferase and fructan:fructan fructosyltransferase were isolated from the inner leaf bases of bulbing onion plants (Allium cepa) and separated by gel filtration on Bio-Gel P-150. Sucrose:sucrose fructosyltransferase produced only one trisaccharide, 1^F-fructosylsucrose, from sucrose. Fructan:fructan fructosyltransferase produced tetrasaccharide and higher polymers from trisaccharide. The trisaccharide found in the greatest concentration in onion, 6^G-fructosylsucrose, was produced from 1^F-fructosylsucrose by fructan:fructan fructosyltransferase and was not a product of sucrose:sucrose fructosyltransferase.     

Ultrastructural cytochemistry of atrial muscle cells

Summary Sections of atrial cardiocytes from young rats were subjected to radioautography after a single intravenous injection of L-leucine-4,5 ³H to identify the sites of synthesis and to follow the migration of newly-formed proteins. As early as 2 min after injection of L-leucine ³H, the label was highest in the rough endoplasmic reticulum (RER), suggesting that cisternal ribosomes are sites of protein synthesis. By 5 min, most of the label had migrated from the RER to the Golgi complex. Some label was already present over specific granules by 2 min but the peak was reached at 1 h. By 4 h, the label over the specific granules had diminished, possibly indicating a release of newly-synthetized secretory material outside the cell. The label over myofilaments and Z-bands was relatively high at most time intervals, suggesting an early and important incorporation of leucine into the contractile and structural proteins of these organelles. The label over the cytosol was initially high and increased even further at 5 and 20 min but decreased to a very low level at 4 h. In contrast, the label over the cell surface rose continuously and peaked at 4 h. The pattern of increment of the label over the cell surface suggests that the newly-formed proteins of these sites are also synthetized in the RER, pass through the Golgi complex and are transported in the cytosol before reaching their destination.     

Synthesis of nitrogenase by isolated heterocysts

Heterocysts isolated from Anabaena variabilis incorporate [¹⁴C]leucine and [³⁵S]methionine into trichloroacetic acid-precipitable material in the light. Analysis by polyacrylamide gel electrophoresis shows that the radioactivity is present in polypeptides of discrete sizes. However, the relative proportions of different proteins synthesized by isolated heterocysts differ from the relative proportions of those proteins incorporated by the heterocysts in intact filaments. The two components of nitrogenase are among the proteins synthesized by the isolated heterocysts.