Effects of 1-palmitoyl-sn-glycero-3-phosphorylcholine on the properties of a solubilized sialyltransferase activity from mouse liver.

Asialomucin-sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity was solubilized from mouse liver microsomes by sonication. The catalytic activity was markedly inhibited by a series of lysophosphatidylcholines, particularly 1-palmitoyl-sn-glycero-3-phosphorylcholine. This lysophospholipid did not alter optimal conditions for enzyme activity. In contrast, it was found that affinities for binding of Mn2+, desialylated mucin and CMP-sialic acid were decreased by adding the lipid. A reasonable interpretation of these data is that the presence of phospholipid modifies the enzyme conformation.

Breaks in arrhenius plots of reactions involving membrane-bound and solubilized sialyltransferases, due to temperature dependence of kinetic parameters.

Temperature dependence of asialomucin-sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity is investigated. Discontinuities in Arrhenius plots are observed, whether the enzyme is membrane-associated or solubilized. These discontinuities cannot be firmly correlated with the phase-transition temperatures of either endogenous or exogenous phospholipids. Arrhenius plots of the kinetic parameters also exhibit sharp discontinuities, so that it is concluded that a significant change in Km and Vmax values occurs with varying temperature. Our results suggest that the biphasic behavior of Arrhenius plots may be attributed to the temperature dependence of the kinetic parameters for both membrane-associated and solubilized sialyltransferase activities.

Temperature dependence of membranous and solubilized sialyltransferase activities in the presence of 1-palmitoyl-sn-glycero-3-phosphorylcholine and fatty acids.

The temperature dependence of sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetyl-neuraminyltrasferase, EC 2.4.99.1) inhibition is described when 1-palmitoyl-sn-glycero-3-phosphorylcholine, or a saturated fatty acid (lauric, myristic or palmitic acid) or an equimolar mixture of the two components are added. Lysophospholipid and fatty acids have no appreciable effect on the optimal temperature for sialyltransferase activity. In the presence of lysophospholipid, the membranous sialyltransferase activity is decreased for all the temperature range tested. In contrast, the solubilized sialyltransferase activity is decreased for temperatures exceeding 29 degrees C. In the presence of saturated fatty acids, the membranous activity is decreased above a chain-length dependent temperature: 22 degrees, 25 degrees and 30 degrees C for lauric, myristic and palmitic acids, respectively. In contrast, the solubilized activity remains unchanged. In the presence of equimolar mixtures of lysophospholipid and fatty acid, the membranous activity is decreased above the same critical temperature as that described for fatty acids added alone. In contrast, the solubilized activity is decreased above 29 degrees C. From these observations, it is suggested that lysophospholipid inhibits the solubilized enzyme when the temperature exceeds the critical micellar temperature of this lipid. The fatty acids inhibit the microsomal enzyme probably by incorporating into the membrane. It is also suggested that equimolar mixtures of lysophospholipid and fatty acid give rise to molecular analogs of 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine.

[Production of interferon and alpha 2-macroglobulin involvement in immune response during human viral hepatitis A (author's transl)]. / Production d'interféron et participation de l' alpha 2-macroglobuline à la réponse immunologique au cours de l'hepatite virale humaine de type A.

In viral hepatitis A, we could distinguish between monophasic and polyphasic forms. Monophasic and polyphasic hepatitis A induce the production of plasma interferon. Interferon level, elevated as early as the first days following the appearance of clinical signs, decreases and reaches a minimum value on the seventh day. A new rise of interferon is characterized by a maximum level on the twelfth day and a minimum level on the thirtieth. Beyond the first month we could still detect the presence of interferon. In the two forms of hepatitis, a complement system is activated both by classical and alternate pathways. IgM levels increase early, IgA levels remain unchanged. On the other hand, IgG levels, only slightly elevated in monophasic hepatitis A, are highly increased in polyphasic hepatitis A beyond the first month. Alpha 2-macroglobulin reaches levels above normal during convalescence in monophasic hepatitis A; on the contrary, in polyphasic hepatitis A, alpha 2-macroglobulin levles are above normal as early as the thirty first days of illness and remain above normal for several months. Elevated levels in alpha 2-macroglobulin may inhibit cellular immunity which is accountable for immunological injury of virus infected hepatocytes. We wonder whether this earlier increase in alpha 2-macroglobulin is responsible for the lasting character of viral infection observed in polyphasic hepatitis A.

Effects of defined synthetic phospholipids on glycosylation processes. Modifications of membrane-bound N-acetylglucosaminyl-transferase and solubilized sialyl-transferase activities.

In this paper, we study effects of phosphatidylcholine synthetic derivatives on two different glycosyltransferasic systems, a membranous mitochondrial N-acetylglucosaminyl-transferase and a solubilized microsomal sialyl-transferase. From all our results, we proved the strong inhibitory effect of lysophosphatidylcholines in these glycosylation processes. We investigated then the relationship between this inhibitory effect and the chemical structure of the studied phospholipids. From this work, it became obvious that the most important inhibitory effect is obtained with a molecule containing a long aliphatic side chain in sn-1 of glycerol, a carbon atom devoid of any large group in sn-2 and an hydrophilic part in sn-3 (specially choline).

Biochemical evidence for the role of alkyl-lysophospholipids on liver sialyltransferase.

Antineoplastic alkyl-lysophospholipids were found to exert a strong inhibitory effect on membranous or solubilized asialomucin-sialyltransferase (CMP-N-acetylneuraminate: D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity. This inhibitory effect was dependent on the presence of the choline moiety in position 3 of the glycerol molecule, as well as on the presence of long ether-linked aliphatic side chain in position 1 and the absence of any large substituent in position 2. As an example, 1-octadecyl-2-O-methyl-glycero-3-phosphorylcholine acted as a mixed-type inhibitor. Such an inhibitory process on sialyltransferase activity might be an additional factor in the tumor cell destructive effect of alkyl-lysophospholipids.