PubMed HealthSearch

PubMed · 7141004

The leukocyte complement system.

Abstract

The existence of a leukocyte complement system is suggested by the findings that certain lymphocytes and mononuclear phagocytes activate complement, express membrane receptors specific for complement activation fragments, and synthesize complement proteins. In this review, attention is directed toward studies indicating that complement proteins may be expressed on the surface of lymphocytes and monocytes, the mechanisms by which complement is activated by leukocytes, and the possible role(s) of this cellular complement system in processes by which lymphocytes are stimulated and monocytes are activated to increased cellular activity.

Explore related subjects

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

J S Sundsmo. 1982. The leukocyte complement system.. https://pubmed.ncbi.nlm.nih.gov/7141004/

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

Bacterial triterpenoids of the hopane series from the prochlorophyte Prochlorothrix hollandica and their intracellular localization.

35-O-beta-Galacturonopyranosyl-, 35-O-beta-3,5-anhydro-galacturonopyranosyl- and 35-O-alpha-altruronopyranosylbacteriohopanetetrol accompanied by their 2 beta-methyl homologues have been isolated from Prochlorothrix hollandica. We report here C35 triterpenoids of the hopane series in a prochlorophyte, a group of prokaryotic oxigenic phototrophs of the cyanobacterial lineage. Like many cyanobacteria, P. hollandica contains a mixture of non-methylated as well as 2 beta-methylhopanoids. After side-chain cleavage by periodic acid oxidation followed by sodium borohydride reduction, these hopanoids could be localized in cell walls and thylakoids, in accordance with their role as membrane stabilizers.

Cell Compartmentation

Mutations in the PAY5 gene of the yeast Yarrowia lipolytica cause the accumulation of multiple subpopulations of peroxisomes.

We previously reported the cloning of the PAY5 gene of the yeast Yarrowia lipolytica by complementation of the peroxisome assembly mutant pay5-1 (Eitzen, G. A., Titorenko, V. I., Smith, J. J., Veenhuis, M., Szilard, R. K., and Rachubinski, R. A. (1996) J. Biol. Chem. 271, 20300-20306). The peroxisomal integral membrane protein Pay5p is a homologue of mammalian PAF-1 proteins, which are essential for peroxisome assembly and whose mutation in humans results in peroxisome biogenesis disorders. Mutations in the PAY5 gene result in the accumulation of three distinct peroxisomal subpopulations. These subpopulations are characterized by differences in 1) buoyant density, 2) the relative distribution of peroxisomal matrix and membrane proteins, 3) the efficiency of import of several peroxisomal matrix proteins, and 4) the phospholipid levels of peroxisomal membranes. These data, together with the analysis of temporal changes in the relative abundance of individual peroxisomal subpopulations in pay5 mutants, suggest that these subpopulations represent intermediates in a multistep peroxisome assembly pathway normally operating in yeast cells.

Cell Compartmentation

The ubiquitin-activating enzyme E1 is phosphorylated and localized to the nucleus in a cell cycle-dependent manner.

The ubiquitin-activating enzyme E1 exists as two isoforms, E1a (117 kDa) and E1b (110 kDa). E1a is phosphorylated, whereas E1b is not. In the present study we have demonstrated the cell cycle dependence of E1a phosphorylation: a 2-fold increase in the specific phosphorylation of E1a in G2 compared with the basal level of phosphorylation in the other stages of the cell cycle. Two-dimensional gel electrophoresis resolved E1 into the two isoforms E1a and E1b; E1a resolved further as three phosphorylated forms and one nonphosphorylated form, while E1b resolved as one nonphosphorylated form. E1a is found predominantly in the phosphorylated forms. However, the distribution of E1a among these different phosphorylated forms was not cell cycle-dependent. We next evaluated the enzymatic activity of E1 as well as its subcellular localization throughout the cell cycle. 32P-Pyrophosphate exchange activity of E1 did not vary along the cell cycle; however, the amount of ubiquitin-protein conjugates decreased by 50% in G2. Nuclear and cytosolic fractionation of cells revealed the nuclear to cytosolic ratio of phosphorylated E1a was 3-fold greater in G2 compared with the other stages of the cell cycle. Finally, purified nuclear extracts supported E1-dependent ubiquitin conjugation of exogenous substrates as did purified cytosol. However, in nuclear extracts but not in cytosol the amount of E1 activity was rate-limiting. Thus we establish nuclear E1-dependent protein ubiquitination and propose that an increase in phosphorylation of E1a in G2 functions to increase the import and/or retention of E1a in the nucleus and may modulate nuclear protein ubiquitination.

Cell Compartmentation