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.).     

Comparison of Undefined Medium and Its Dialyzable Fraction for Growth of Mycoplasma

In examining the medium used in cultivation of Mycoplasma for deoxyribonucleic acid isolation, it was found that an aggregate was present which sedimented with the organisms and which was ethyl alcohol-precipitated during deoxyribonucleic acid purification. To eliminate the contaminating material, a method was devised to obtain only the dialyzable constituents of the medium. This report describes the preparation of a dialysate of soy peptone-yeast extract. The medium, obtained by immersion of the encased dehydrated ingredients in sodium chloride solution for 5.5 hr at approximately 80 C, has been employed as the basal medium for cultivation of a number of Mycoplasma species. Comparative growth curves of two saprophytic strains and two parasitic species indicated that multiplication in dialysate, with suitable supplement, followed the pattern typical of the common eubacteria. Thus, by elimination of the sediment which occurred in nondialyzed medium, Mycoplasma could be concentrated without concomitant accumulation of contaminating macromolecules.     

Deoxyribonucleic Acid Homology and Relative Genome Size in Mycoplasma

The deoxyribonucleic acid homologies of Mycoplasma laidlawii type A and type B, M. pulmonis (#47 and #63), and M. hominis were determined by membrane methodology. The homology data revealed a difference in genome size between M. laidlawii type A and type B. This difference also held with stringent conditions of annealing (high temperature). Little or negligible homology was shown to exist between the M. laidlawii strains type A and type B and M. pulmonis strains 47 and 63 and M. hominis. M. hominis showed less than 10% homology to the M. pulmonis and M. laidlawii strains. Neither of the M. laidlawii strains showed more than 2% annealing to the M. pulmonis strains. Reaction rate studies are suggested as a means of demonstrating the phylogenetic relationship between the Mycoplasma and other microorganisms.     

Nitrogen chlorosis in blue-green algae

Summary Nitrogen deficient Anacystis nidulans contained normal levels of chlorophyll-a and carotenoids but did not contain any phycocyanin. These organisms also contained large amounts of polysaccharide. The addition of nitrate to a deficient culture resulted in the recovery of normal pigmentation over a period of several hours.The relation between these changes and growth was established by a kinetic study of the changes in cell composition during pigment loss and recovery. Loss of phycocyanin commenced with the cessation of growth due to nitrogen limitation and was complete after 15 hours. In contrast there were only minor changes in chlorophyll-a and carotenoid. After growth had ceased polysaccharide continued to increase and viability dropped sharply although total cell counts did not change. These trends were reversed by the addition of nitrate to deficient cultures. Phycocyanin was detected after a short lag and normal levels of phycobiliprotein were present within 8 hours. Cell division did not begin until normal levels of phycocyanin had been restored. During the recovery of normal pigmentation there was a decrease in reducing sugar content and a sharp rise in viability. Qualitative studies with 9 additional blue-green algae suggest that loss of phycocyanin is a characteristic feature of nitrogen deficiency in blue-green algae.     

BONE MARROW RESTORATION AFTER LOCALIZED DEPLETION

Studies have been made of marrow restoration after localized depletion of the rabbit femur by dextran perfusion. Restoration was shown to involve an initial period of reorganization which blends with a more prolonged period of hemic cell repopulation. Cellularity returned to normal levels by 35 days, the recovery of myeloid cells being somewhat more rapid than that of the erythroid elements. In either case, the evolution of immature hemic cells was soon followed by the appearance of more mature forms even at the earliest stages of marrow repopulation. ³H-TdR uptake per cell increased rapidly to a level approximately twice normal after the first week. The augmented incorporation of thymidine, revealed by scintillation spectrometry and confirmed upon autoradiography, was shown to be due to an increase in DNA synthesis rate as well as in the fraction of participating cells. It is suggested that the enhanced cell production is brought about by a decrease in the proliferative cell cycle and an increase in the growth fraction. The origin of the repopulating cells remains a moot point. Cell migration from the epiphyseal marrow is apparently not involved. Irrespective of the source of stem-type cells, the stimulus for regeneration appears to be locally determined.     

Two Additional Salmonella Serotypes: Salmonella enteritidis Ser 58:a:- and Salmonella enteritidis Ser 44Z36, Z38:-

The antigenic compositions of two additional Salmonella serotypes isolated from the feces of man were determined to be 58:a:- and 44:Z(36), Z(38)-.     

Acetamide Agar Medium Selective for Pseudomonas aeruginosa

A synthetic base of acetamide and salts in agar permitted isolation of small numbers of Pseudomonas aeruginosa from swarming Proteus and other gram-negative species.     

Methacarn (methanol-Carnoy) fixation

Summary According to chemical data, methanol raises the shrinkage temperature of collagen significantly more than ethanol (86° C versus 70° C). Since increase of shrinkage temperature appears desirable in tissues to be embedded in paraffin, methanol was substituted for ethanol in Carnoy's fluid. This methanol-Carnoy mixture is referred to as methacarn solution. The fixation-embedding procedure was similar to that described in the study of Carnoy fixation. Methacarn-fixed sections showed little or no shrinkage and compared well with material fixed in Carnoy's or Zenker's fluid. Myofibrils, especially in endothelial and epithelial cells, were more prominent in methacarn- than in Carnoy-fixed tissues.A review of the chemical literature showed that methanol, ethanol and chloroform stabilize or even enhance helical conformations of proteins, presumably by strengthening of hydrogen bonds. Interference with hydrophobic bonds causes unfolding and/or structural rearrangements in globular proteins. The twin-helical structure of DNA collapses in alcoholic solutions. Hence, methacarn fixation can be expected to preserve the helical proteins in myofibrils and collagen, but the conformations of globular proteins and DNA will be significantly altered. Literature on conformational effects produced by fixatives used in electron microscopy was also reviewed. Glutaraldehyde and OsO₄ cause considerable loss of helix (22–29% and 39–66% respectively). KMnO₄ and glutaraldehyde followed by OsO₄ produce extensive transitions from helical to random-coil conformations similar to those seen in powerful denaturants such as 8 M urea. Evidently these fixatives are unsuitable for studies of helical proteins. In contrast ethylene glycol preserves helical conformations.     

Photosynthetic Membrane System in Anacystis nidulans

Cultures of Anacystis nidulans were grown under conditions of varying light intensity and temperature. Changes in pigment content were compared with changes in the fine structure of these cells. Pigment concentration and lamellar content varied inversely with the light intensity in cells grown with 100 and 1,000 foot candles of fluorescent light. Estimations of the relative area and volume of lamellae in cells showed that the amount of double membrane was directly proportional to the chlorophyll content of whole cells. Continuity of double membranes with cytoplasmic membrane was observed.