Human brain gangliosides: developmental changes from early fetal stage to advanced age

The developmental profiles of the four major brain gangliosides, GM1, GD1a, GD1b, and GT1b, were examined in human frontal lobe covering the period from 10 fetal weeks to 80 years of age. The ganglioside concentration increased approx. 3-fold from the 10th gestational week to the age of about 5 years. Gangliosides GM1 and GD1a increased 12-15-fold during the same period. The most rapid increase of GM1 and GD1a occurred around term, during the period for dendrite arborization, outgrowth of axons and synaptogenesis. GT1b showed a quite different developmental curve. It was the major ganglioside during the 3rd to 5th gestational month, whereafter its concentration dropped rapidly to term, from which time the concentration then increased up to 50 years of age. Similar curves were found for the other gangliosides of the b-series, GD3, GD2, GD1b and GQ1b. Ganglioside 3'-isoLM1 was a characteristic early fetal ganglioside which dropped rapidly to the 5th gestational month, reached a small peak around term and then disappeared during adulthood. The concentration of gangliosides of the neolacto series was larger than that of the lacto series during the whole developmental period. In the beginning of the second trimester, 3'-LM1 constituted 2% and LD1 10% of total ganglioside sialic acid. The new findings demonstrate more dynamic changes of the ganglioside patterns during development than noted in previous studies.     

Pulse-chase studies of the synthesis and intracellular transport of apolipoprotein B-100 in Hep G2 cells

The synthesis and secretion of apolipoprotein B-100 (apoB-100) have been studied in a human hepatoma cell line, the Hep G2 cells. The time needed for the synthesis of apoB-100 was estimated to be 14 min, which corresponds to a translation rate of approximately 6 amino acids/s. ApoB-100 was compared with albumin and alpha 2-macroglobulin as to the distribution between the membrane and the luminal content in the endoplasmic reticulum (ER) and the Golgi apparatus. The results suggested that apoB-100 approximately followed the distribution of these secretory proteins in the Golgi, while the ratios between the percent membrane-bound apoB-100 and percent membrane-bound albumin or alpha 2-macroglobulin were 3-4:1 in the ER. This may suggest that apoB-100 occurs in a membrane-associated form in ER prior to the integration in the lipoproteins. Pulse-chase studies combined with subcellular fractionation was used to investigate the kinetics for the intracellular transfer of apoB-100. A 3-min pulse of [35S]methionine was followed by an increase in apoB-100 radioactivity in the ER during the first 10-15 min of chase. The following 10-15 min of chase were characterized by linear decrease in apoB-100 radioactivity with a decay rate of approximately 6%/min. The residence kinetics for apoB-100 in the ER differed from that of transferrin and probably also from that of albumin. By comparing the time for the pulse maximum in ER with that in the denser Golgi fractions the time needed for the transfer between ER and Golgi could be estimated to be 10 min. The time needed for the secretion of newly synthesized apoB-100 was estimated to be 30 min. This indicates that the transfer of the protein through the Golgi apparatus to the extracellular space requires 20 min.     

Membrane lipids of human peripheral nerve and spinal cord.

Major membrane lipids were determined in specimens of human peripheral nerve (cauda equina) and spinal cord of 10 subjects aged 20-70 years. The same lipids were also assayed in myelin from the same tissues isolated with two different procedures and in myelin of cauda equina from 3 subjects aged 17-91 years isolated with a third method. The concentrations (mean and standard deviation) of phospholipids were 90 +/- 11 and 96 +/- 9 nmol/g fresh weight; of cholesterol 70 +/- 15 and 101 +/- 16; of cerebroside 19 +/- 3 and 41 +/- 7; of sulfatide 10 +/- 1 and 11 +/- l; and of gangliosides 0.80 +/- 0.08 and 0.40 +/- 0.05 N in cauda equina and spinal cord, respectively. The proportion of ethanolamine phosphoglyceride was lower and that of sphingomyelin higher in cauda equina than in spinal cord. The myelin of peripheral nerve and spinal cord contained almost the same proportions of lipids as the whole tissue. The protein-bound sialic acid content was 3-fold higher than the lipid-bound sialic acid content in cauda myelin. The fatty acid patterns of choline, ethanolamine, inositol and serine phosphoglycerides of spinal cord and its myelin, were very similar to those of cerebral white matter, while the phosphoglycerides of cauda equina had higher proportions of monoenoic acids and lower proportions of polyunsaturated fatty acids. The fatty acid patterns of sphingomyelin, cerebroside and sulfatide of spinal cord were similar to those of cerebral white matter, while those of cauda equina contained significantly more saturated fatty acids. This suggests that the lipid and fatty acid compositions of peripheral nerve are particularly suitable for the formation of a tightly packed myelin membrane which can be a powerful shield against infections and other injuries.     

Evidence for a structural relationship between apoB75kDa and human plasma apolipoprotein B 100, from translation of human liver mRNA in vitro and immunochemical studies with monoclonal and polyclonal antibodies

The report deals with a detailed balance of ATP production and consumption of the rabbit reticulocyte. The sum-total of ATP produced amounts to 135 mmol . 1-1 . h-1. About 70% of the ATP consumption has been accounted for by specific processes. The main contributing processes are the globin synthesis with about 28%, the Na+, K+-ATPase with 23% and the proteolysis with more than 15%. 30% of ATP consumption has not been accounted for. Cycloheximide (20 microM) leads to a dissociation between synthesis and degradation of proteins, which argues against any obligatory connection between these processes. More than 90% of the lysine liberated from mitochondria by proteolysis were reutilized for the globin synthesis demonstrating the high nitrogen economy of reticulocytes. Each of the ATP-consuming processes studied appears to control ATP production in an independent manner without competition with each other.     

Streptococcus pyogenes in human plasma: adaptive mechanisms analyzed by mass spectrometry-based proteomics

Streptococcus pyogenes is a major bacterial pathogen and a potent inducer of inflammation causing plasma leakage at the site of infection. A combination of label-free quantitative mass spectrometry-based proteomics strategies were used to measure how the intracellular proteome homeostasis of S. pyogenes is influenced by the presence of human plasma, identifying and quantifying 842 proteins. In plasma the bacterium modifies its production of 213 proteins, and the most pronounced change was the complete down-regulation of proteins required for fatty acid biosynthesis. Fatty acids are transported by albumin (HSA) in plasma. S. pyogenes expresses HSA-binding surface proteins, and HSA carrying fatty acids reduced the amount of fatty acid biosynthesis proteins to the same extent as plasma. The results clarify the function of HSA-binding proteins in S. pyogenes and underline the power of the quantitative mass spectrometry strategy used here to investigate bacterial adaptation to a given environment.