The presence of lysophosphatidylcholine in chromaffin granules

Lysophosphatidylcholine is thought to be a characteristic component of the chromaffin granules in adrenal glands. By the use of a t.l.c. system that resolves minor phospholipids satisfactorily, this subcellular location was confirmed in the present study in bovine glands. However, phospholipid degradation was demonstrated in homogenates of the adrenal medulla and cortex under conditions similar to those of subcellular fractionation (incubation at 4°C for 90min). Phosphatidylethanolamine and cardiolipin were hydrolysed, but the concentration of lysophosphatidylcholine did not change, indicating that the latter was present in the medulla before this treatment. Attempts were made to decrease the time between death of the animal and the extraction of lipids. Lysophosphatidylcholine was easily demonstrable in lipid extracts of the dissected medulla and even in those of the whole bovine gland. For practical reasons it is not possible to decrease further the time lapse before extraction in the case of this animal. Adrenal glands were obtained from anaesthetized and untreated rabbits. These were frozen immediately in liquid N₂ and the lipids were extracted. In a control experiment, the glands from rabbit were dissected and treated in the same manner as with those of ox, and then the lipids were extracted. No lysophosphatidylcholine was detected in the extracts from glands frozen in liquid N₂ but lysophosphatidylcholine was observed in the controls. These results suggest that lysophosphatidylcholine is not a component of chromaffin granules, but is produced if the period between death of the animal and lipid extraction is unduly prolonged. To discover whether lysophosphatidylcholine affected the permeability barrier properties of chromaffin granules, sonicated liposomes of egg phosphatidylcholine alone or with lysophosphatidylcholine (15mol/100mol) were prepared. Both types were shown by electron microscopy to be largely made up of single bilayer vesicles. The exchange diffusion of [¹⁴C]dopamine was measured across their membranes. Both types of liposomes had similar capture volumes (0.5μl/μmol of phospholipid), and the activation energies of the exchange diffusion of dopamine were also similar (31kJ/mol). These results indicate that the presence of this proportion of lysophosphatidylcholine in chromaffin-granule membranes is not likely to influence their barrier properties towards catecholamines.     

The location of phosphorylation sites and Ca2+-dependent proteolytic cleavage sites on the major neurofilament polypeptides from Myxicola infundibulum.

1. When axoplasm is incubated with [32P]Pi the main phosphorylated components are the neurofilament polypeptides. 2. Activation with Ca2+ of the proteinase present in axoplasm causes degradation of these neurofilaments and the peptides produced by this reaction have been analysed by fingerprinting. 3. Fingerprinting shows that initially the Ca2+-activated proteinase cleaves the neurofilament polypeptides at three major sites producing polypeptides with mol.wts. 70,000, 50,000 and 47,000. 4. These polypeptides sediment with filaments, originate from the tail-region of the molecule and contain a little radioactive label. 5. As these polypeptides are produced, other polypeptides that come from the head-region of the molecule are liberated as soluble products that contain the bulk of the radioactivity. 6. Fingerprinting therefore shows that at least two regions on the molecule are phosphorylated and that the major one is located towards the head-end of the polypeptides.     

Anomalies physio-morphologiques de la souche virosée (Bali 1) d'Allomyces arbuscula

An escape reaction of the hyphae from virus-containing strain Bali 1 of A. arbuscula was detected when intra- and interspecific Allomyces cultures were opposed on solid media. Hyphae of this virus-containing strain proliferate into witch-broom structures only detectable on solid media in which bunches of rhizoid-like structures remain more superficial than those of the control cultures, suggesting that metabolism of the Bali 1 strain is altered into a more aerobic type.     

Chronotropism and blood flow patterns following teratogenic doses of catecholamines in 5-day-old chick embryos.

In vivo heart rates of 5-day-old chick embryos were recorded from electrodes placed in close proximity to the heart. L-epinephrine (4X10(-10) mole), 1-norepinephrine (1X10(-9)mole) and 1-isoproterenol (1.6X10(-10)mole) in 5 microliter of isotonic saline transiently accerlerated the mean heart rate by almost 9 percent. L-phenylephrine (2X10(-9)mole/5microliter) and the experimental procedure produced no appreciable effect. The positive chronotropic effect of the catecholamines was found to be highly significant (P less than 0.0005) as computed by Student's t test. However, no direct relationship could be established between the chronotropic response and the aortic arch anomalies produced. A prolonged reduction of blood flow in the primitive heart tube and the sixth aortic arch after administration of epinephrine and isoproterenol is apparently related to the induction of hypoplastic right pulmonary artery with absent or hypoplastic right ductus arteriosus.     

RIBOSOMAL ACTIVITY IN PRENATAL MOUSE BRAIN

Abstract— Regulation of protein synthesis is important for the proper growth and development of the brain. Our previous work on the regulation of protein synthetic activity in fetal mouse brain cell suspensions showed that the rate of protein synthesis decreased during the prenatal period. In the present study, ribosomal activity of cell-free homogenates and purified ribosomes obtained from fetal neural tissue was measured. The post-mitochondrial supernatant (PMS) fraction actively incorporated amino acids into polypeptides using either endogenous mRNA or polyuridylic acid as template. The protein synthetic activity was dependent upon the age of the fetus. Ribosomes purified from this fraction were also active in protein synthesis. Incorporation of phenylalanine was linear for 20 min, and dependent upon the concentration of ribosomes and the pH 5 enzyme fraction. The age dependent decrease in protein synthetic activity observed with the post-mitochondrial supernatant fractions was not found when these purified ribosomes were employed. Ribosomes obtained from fetal, newborn or adult neural tissue were compared and found equally active in their protein synthetic capacity.     

MICROHETEROGENEITY OF BRAIN CYTOPLASMIC AND SYNAPTOPLASMIC ACTINS

Abstract— Actin present in whole rat brain cytoplasm and in synaptosomes was purified by DNase I affinity chromatography. By use of two-dimensional gels and one-dimensional isoelectric focusing gels, brain actin was shown to be composed of two isomeric forms. By comparison with muscle actins, brain actins were identified as the β and γ isomers. Muscle type α actin is not present in brain. Synaptosomal protein with high affinity for DNase I is primarily composed of β and γ actin, however, two minor synaptosomal proteins, S₁ and S₂, with similar DNase I affinity were also isolated. S₁1 and S₂ have the same apparent molecular weight as whole brain actin, are more acidic than the major actin forms and are distinct from a actin. Relative to β and γ actin, the content of S₁ and S₂ is 3-fOld greater in synaptosomes when compared to similar non-synaptosomal species. The results demonstrate heterogeneity of brain actins and compartmentalization of brain proteins with high affinity for DNase I at the synapse. It was also shown that tubulin has selective affinity for the DNase I-actin complex.