Cold stress induces in situ phospholipid molecular species changes in cell surface membranes

The structural organization of Tetrahymena pyriformis is such that its cilia are remote from the main centers of lipid metabolism. As a result, the ciliary membrane lipid composition of cells exposed to low-temperature stress is initially unaffected by the significant metabolic changes induced in microsomal membranes. Nevertheless, changes in the ciliary membrane lipid composition can be detected during the first 4 h of cold exposure. A combination of in vivo and in vitro experiments has provided strong evidence for a substantial retailoring of ciliary phospholipid molecular species in situ in the absence of any importation of lipids from the cell interior or change in overall ciliary fatty acid composition. The mechanism responsible for the ciliary lipid changes is independent of the one(s) triggering internal acclimation responses. Our observations establish for the first time that chilling stress can simultaneously induce separate and distinctive lipid modification responses in different parts of a cell. This finding could be important in identifying the molecular ‘sensor’ capable of actuating stress-induced lipid changes.     

Crosslinking of chromosomal proteins to DNA in HeLa cells by UV gamma radiation and some antitumor drugs

Immunochemical techniques were used to investigate the protein-DNA crosslinking by ultraviolet (UV) and gamma radiation as well as 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) or cis- and trans-diamminedichloroplatinum II (cis-DDP and trans-DDP). Antisera to 0.35 M NaCl extract and 0.35 M NaCl residue of HeLa nuclei were employed. Both gamma and UV irradiation, exposure to cis- or trans-DDP and, to a lesser extent, BCNU, resulted in crosslinking of various antigens to the DNA. Although several antigens were crosslinked by all the employed agents, other exhibited agent-specific crosslinking patterns.     

Amino acid sequence homology between rat prostatic steroid binding protein and rabbit uteroglobin

Using a computer program designed to detect evolutionary relationships between proteins, I find that the polypeptide chain of rabbit uteroglobin has amino acid sequence homology with the C1 and C2 polypeptide chains of rat prostatic steroid binding protein. Using this finding I suggest several interesting approaches for studying the biology of these proteins.     

Binding of 8-bromoguanylic acid to ribonuclease T1 as studied by absorption and circular dichroism spectroscopy

8-Bromoguanosine 2'- and 3'-phosphates have been shown to bind to RNase T1 with the same affinity as the corresponding guanosine phosphates, inducing difference absorption and circular dichroism spectra similar to those induced by the guanosine phosphates. Since the brominated ligands have reduced electron density on N-7 of the guanine ring and syn-fixed conformation due to a bulky, electron-withdrawing Br substituent on C-8, the difference spectra are not attributable to the protonation on N-7 and to the restriction of the ligand to syn-conformation as proposed previously.     

Beta-adrenergic stimulation evokes a rapid, Ca2+-dependent stimulation of endocytosis, hexose and amino acid transport associated with increased Ca2+ fluxes in mouse kidney cortex

The beta-adrenergic agonist 1-isoproterenol evokes an acute (less than 5 min) stimulation of endocytosis, hexose transport and amino acid transport, measured by the temperature-sensitive uptake of HRP, 3H-DG and 14C-AIB, in mouse kidney cortex slices. This stimulation is concentration dependent and is maximal at 10(-8)-10(-7) M isoproterenol. Peroxidase cytochemistry showed that the hormonal increase in HRP uptake is confined to proximal tubules. The rapid membrane response is abolished in a calcium-free medium and by the beta-adrenergic antagonist propranolol, indicating Ca2+- and beta-adrenoreceptor-dependence. Isoproterenol (1 microM) rapidly (less than 30 sec) stimulates the influx and efflux of 45Ca in cortex slices. Isoproterenol also decreased mitochondrial 45Ca and increased soluble 45Ca. These results indicate that beta-adrenergic stimulation of membrane transport functions involves an increased influx of extracellular calcium and a mobilization of intracellular (mitochondrial) calcium. An increase in cytosolic Ca2+ concentration appears to be the regulatory signal for these membrane transport processes.     

Effects of 5'deoxy-5'-methylthioadenosine on the metabolism of S-adenosyl methionine

The treatment of transformed rat cells with micromolar amounts of 5'deoxy 5'methyl thioadenosine induces rapid effects on the rate of methylation of DNA concomitantly with alterations of intracellular pools of S-adenosyl methionine and S-adenosyl homocysteine. Pulse chase labelling experiments indicate that 5'deoxy 5'methylthioadenosine does not inhibit the degradation of S-adenosyl homocysteine but inhibits the consumption of S-adenosyl methionine. In vitro transmethylation assays performed with heterologous DNA show that low doses of the thioethernucleoside do not significantly affect the DNA methyltransferase activity of cellular extracts. The biological role of 5'deoxy 5'methylthioadenosine, a natural molecule formed during the synthesis of polyamines is discussed.     

ADP- and epinephrine-elicited release of [3H]guanylylimododiphosphate from platelet membranes: Implications for receptor-Ni stoichiometry

Epinephrine-promoted release of [³H]guanylylimidodiphosphate ([³H]Gpp(NH)p) from human platelet membranes has been used to probe the interactions between alpha₂-adrenergic recpetors and N_i, the guanine nucleotide binding protein that couples those receptors to an inhibition of adenylate cyclase activity. We show here that ADP, which also acts through specific platelet receptors to inhibit adenylate cyclase activity, also promotes the release of [³H]Gpp(NH). The amount of [³H]Gpp(NH)-release elicited by epinephrine and by ADP together is equal to the sum of the amounts released by the two agents acting individually. Furthermore the maximal amounts of [³H]Gpp(NH)-release elicited by each of the two agents approximates the numbers of receptors for ADP and epinephrine present in the platelet membranes. These results suggest that the two receptor types interact with distinct portions of the pool of N_i molecules and that each receptor initiates guanine-nucleotide exchange on a single molecule of N_i.     

Induction of 2',5' oligo(A) synthetase in tumor-bearing mice with encephalomyocarditis (EMC) virus or poly(I)poly(C)

Infection of 13 month-old C3H mice with EMC virus or inoculation with the interferon inducer poly(I)poly(C) results in elevated levels of the enzyme 2',5' oligo(A) synthetase only in animals with spontaneous tumors (breast cancer or hepatomas). High enzymatic activities are detected in homogenates from liver, spleen, plasma and neoplastic cells of the animals with breast carcinomas and only in the neoplastic liver cells of the animals with hepatomas.     

Dephosphorylation and reactivation of phosphorylated purified ox-kidney branched-chain dehydrogenase complex by co-purified phosphatase

The branched-chain 2 oxoacid dehydrogenase complex has been purified from well-washed ox-kidney mitochondria together with branched-chain dehydrogenase kinase. The complex was inactivated and phosphorylated by ATP in about 5 min at 30 degrees C. After hydrolysis of ATP by a contaminating ATPase (5-10 min) the complex was dephosphorylated and reactivated. Dephosphorylation and reactivation were linearly correlated. Reactivation was dependent upon Mg2+ (K0.5 greater than 1 mM) and inhibited completely by 50 mM fluoride. Reactivation and dephosphorylation are attributed to a mitochondrial branched-chain dehydrogenase phosphatase.     

Capacitance--voltage relationship in phospholipid bilayers containing gangliosides

Changes in the position of the minimum of the parabolic capacitance-voltage curve allow the measurement of the amount of ganglioside present in artificial bilayers made with phosphatidylcholine-ganglioside mixtures and asymmetrically shielded with Ca2+. The screening effect of the ionic solution must be considered. With ganglioside/phospholipid molar ratios of up to 15%, all glycolipids can be found at the membrane surfaces.