Detergent Effects on the Phosphatidylinositol-Specific Phospholipase C in Rat Brain Synaptosomes

In the presence of Ca2+ (2.5 mM) and using [14C]arachidonoyl phosphatidylinositol (PI) membrane as substrate, phosphatidylinositol-specific phospholipase C (PI-PLC) (EC 3.1.4.10) in rat brain synaptosomes was activated by deoxycholate but not taurocholate. Calcium stimulated enzymic hydrolysis by both detergents, but the stimulatory effect of taurocholate was less than that of deoxycholate. Peak stimulation for deoxycholate was observed at 1 mg/ml, whereas that for taurocholate was 4 mg/ml. When 1 mM EDTA was added to the taurocholate (4 mg/ml) and Ca2+ (3.5 mM) system, synaptosomal PI-PLC activity was greatly stimulated, to almost the same level as the deoxycholate + Ca2+ system. This system required the presence of all three factors, and EGTA could not effectively replace EDTA in the stimulatory action. The detergent-induced hydrolysis of synaptosomal PI by the deoxycholate + Ca2+ and the taurocholate + Ca2+ + EDTA systems was strongly inhibited by divalent metal ions such as Zn2+, Cu2+, Pb2+, and Fe2+, whereas Mg2+ and Ca2+ were ineffective. Nevertheless, only the deoxycholate + Ca2+ system was responsive to enzyme inhibition by membrane-perturbing agents such as lysophospholipids and free fatty acids. The specific requirement for EDTA in the taurocholate system may be due to the release of a pool of inhibitory divalent metal ions from the membranes.     

Correlation between microtubular number and transport activity of hypothalamo-neurohypophyseal secretory neurons

Summary The lower pituitary stalk has been studied in rats given hypertonic saline for four days and in rats with congenital diabetes insipidus (GDI), that is, in two groups of animals in which there is evidence of an increase in the transport of polypeptides down the axons of the tractus hypophyseus.A quantitative ultrastructural analysis of this tract, the first yet made, has demonstrated that in normal animals it is composed of unusually small axons, over half of which are less than 300 nm in diameter.In this tract there is a significant increase in axonal diameter and microtubular content in animals given hypertonic saline for four days. In adult rats with CDI, these changes are even more marked, a feature which is correlated with the fact that in these animals the transport of polypeptides has probably been abnormal since birth.An alteration in the microtubular content of neurons has not previously been observed either in physiologically stressed animals or in diseased animals; such alterations suggest the participation of microtubules in polypeptide transport. The narrow diameter of axons in the tractus hypophyseus of the normal animal raises the possibility of the extravesicular transport of such polypeptides.Abbreviations used ADH antidiuretic hormone - AF aldehyde fuchsin - CDI congenital diabetes insipidus - HNS hypothalamo-neurohypophysiel system - NSM neurosecretory material - NSV neurosecretory vesicle - PVN paraventricular nucleus - SON supraoptic nucleus This paper is dedicated to Professor W. Bargmann.We are grateful to Miss Pauline Chapman for technical assistance.This project is supported by the Medical Research Council.     

THE METABOLISM OF PALMITIC ACID IN THE PHOSPHOLIPIDS, NEUTRAL GLYCERIDES AND GALACTOLIPIDS OF MOUSE BRAIN

Abstract— Following intracerebral injection, [¹⁴C]palmitic acid was rapidly incorporated into a variety of brain lipids. After 12 hr, 78 per cent of the lipid radioactivity was in phospholipids, 15 per cent was in triacylglycerols, 1 per cent each was in free fatty acids and galactolipids, and the remainder was in other neutral glycerides. Over 65 per cent of the phospholipid radioactivity was found in the choline phosphoglycerides but this proportion decreased substantially with time. At later times, increasing portions of the radioactivity were present in the monounsaturated acyl groups and the alkenyl groups but no radioactivity was detected in cholesterol or polyunsaturated acyl groups. These results indicate that most of the extensive recycling of radioactivity took place without oxidative degradation of the palmitoyl groups. The relative rates of incorporation of radioactivity were compared at 12 hr after injection. The specific radioactivities of the serine, ethanolamine, and choline phosphoglycerides had ratios of 6:3:2 based on the palmitoyl group content and 1:2:4 based on their phosphorus content. The specific radioactivities of galactolipids with O -acyl groups were higher than the specific radioactivitiesof cerebrosides or cerebroside sulphates. A new solvent mixture for thin-layer chromatography of brain galactolipids was described (chloroform-acetone-methanol-water, 60:20:20:1, by vol.).     

An unstable locus in soybeans

Summary Investigation of a variegated condition in the soybean variety Lincoln indicates instability at the Y locus. Leaf sectors of chlorophyll-less yellow tissue occur in distinct heritable patterns; some leaves have small flecks of yellow tissue (late occurring mutations) and others possess large areas or whole leaflets (early occurring mutations).There is evidence that this allele, Y ₁₈ ^m , mutates to the wild type, Y, which is green and stable and to the recessive, y, which is yellow and lethal in the seedling condition. (With an increase in the amount of yellow tissue there is an increase in the frequency of lethals.) However, changes from one type to the other are observed, and patterns of variegation representing different states of the instability are described. These depend upon the time and frequency of mutation events.Evidence is presented to support the hypothesis that this instability is controlled by a factor that resides at the locus. Such a factor governs the timing of the mutation events and is related to similar elements in maize, which are part of specific mutable systems. Control of variegation of the Y ₁₈ ^m locus is compared with the models proposed for the cases of instability in maize.

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Zusammenfassung Die Untersuchung eines variegaten Zustandes bei der Sojabohnensorte Lincoln führte zum Nachweis einer Instabilität des Y-Locus. Blattsektoren mit chlorophyllfreiem gelbem Gewebe traten in bestimmten erblichen Mustern auf. Einige Blätter wiesen kleine Flecken gelben Gewebes auf (spät eingetretene Mutationen), während andere große Flächen oder vollständig gelbe Blättchen besaßen (früh eingetretene Mutationen).Es gibt Beweise dafür, daß das entsprechende Allel Y ₁₈ ^m sowohl zum stabilen Wildtypallel Y, mit grünem Phänotyp, als auch zum rezessiv gelben y, das im Sämlingsstadium letal wirkt, mutiert. (Eine Zunahme der Menge gelben Gewebes ist mit einer Zunahme der Letalfrequenz verbunden.) Umwandlungen eines Typs zu einem anderen werden beobachtet und Variegationsmuster beschrieben, die unterschiedliche Stadien der Instabilität verkörpern. Diese hängen von dem Zeitpunkt und der Frequenz der Mutationsereignisse ab.Es werden Beweise vorgelegt, die die Hypothese stützen, daß diese Instabilität durch einen Faktor kontrolliert wird, der sich am Locus befindet. Ein Faktor dieser Art kontrolliert das zeitliche Auftreten der Mutationsereignisse. Er ist mit ähnlichen Elementen des Maises verwandt, die Teile eines spezifisch mutablen Systems sind. Die Kontrolle der Variegation durch den Y ₁₈ ^m -Locus wird mit den Modellen verglichen, die für die Fälle der Instabilität beim Mais vorgeschlagen wurden.

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Joint contribution from the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa (Projects 1335 und 1179) as Journal Paper No. 5635.

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Former Agronomist, Crops Research Division, ARS, USDA, and Professor Iowa State University; now Research Director, Peterson Seed Company.