Biomedical subjects

J P Infante

Publications and source records attributed to J P Infante.

5 recordsLinked to original sources

PubMed1979

Co-ordinate regulation of ethanolamine kinase and phosphoethanolamine cytidylyltransferase in the biosynthesis of phosphatidylethanolamine in rat liver.

Essential-fatty acid deficiency produces a 52% increase in the rate of phosphatidyl-ethanolamine synthesis in rat liver as calculated from results obtained in vivo [Trewhella & Collins (1973) Biochem. Biophys. Acta 296, 34--50]. This flux change was used to test the possible regulatory roles of ethanolamine kinase and of phosphoethanolamine cytidylyltransferase, which are rate-limiting enzymes of the cytidine pathway for the synthesis of phosphatidylethanolamine [Infante (1977) Biochem. J. 167, 847--849]. The results show that essential-fatty acid deficiency produces 50% and 53% increases respectively in the specific activity of these enzymes, accounting for the increased rate of phosphatidylethanolamine synthesis produced by this dietary insufficiency. This evidence leads to the conclusion that ethanolamine kinase and phosphoethanolamine cytidylyl-transferase have co-ordinated regulatory roles in the flux control of the cytidine pathway, and its sphinganine 1-phosphate lyase branch reaction, for the synthesis of phosphatidylethanolamine.

Animals↗

PubMed1978

Control of phosphatidylcholine synthesis and the regulatory role of choline kinase in rat liver. Evidence from essential-fatty acid-deficient rats.

Choline kinase and phosphocholine cytidylytransferase catalyse the rate-limiting steps of the cytidine pathway for the synthesis of phosphatidylcholine [Infante (1977) Biochem. J. 167, 847--849]. Essential-fatty acid deficiency induces a 3.5-fold increase in the specific activity of choline kinase, whereas the specific activity of the cytidylytransferase remains unchanged in rat liver. This change in specific activity accounts for the calculated increase in flux through the cytidine pathway produced in vivo by the same dietary state [Trewhella & Collins (1973 Biochim. Biophys. Acta 296, 34--50], thus confirming the fact that choline kinase has a regulatory role in the cytidine pathway for the synthesis of phosphatidylcholine.

Animals↗

PubMed1978

A novel method for determining equilibrium constants. CTP:phosphorylcholine cytidyltransferase.

A novel method for the determination of equilibrium constants for reversible reactions is described. The method is based on the measurement of initial velocities of isotope transfer for a given substrate-product pair of both the forward and reverse reactions as a function of the mass action of reactants. The reciprocal values of these initial velocities are plotted against the mass action ratios of reactants. The observed Keq is the abscissa of the intersection point of these reciprocal plots, i.e. the mass action ratio at which the initial velocities of isotope transfer for both the forward and reverse reaction are identical, that is, when isotope exchange is occurring. In this manner, an observed Keq of 0.2 was obtained from CTP:phosphorylcholine cytidyltransferase (CTP:cholinephosphate cytidyltransferase, EC 2.7.7.15) at 37 degrees C and pH 7.5 under physiological conditions 1.0 mM free Mg2+ and 0.15 M salt concentration. A comparison of this value with the in vivo mass action of reactants calculated from published data indicates that this reaction is rate-limiting in the rat liver (Infante, J.P. (1977) Biochem. J. 167, 847--849).

Animals↗

PubMed1977

Rate-limiting steps in the cytidine pathway for the synthesis of phosphatidylcholine and phosphatidylethanolamine.

An analysis of the available data on the cytidine pathway for the synthesis of phosphatidylcholine and phosphatidylethanolamine, by the logic derived from the theoretical principles of metabolic regulation, shows that the first two reactions catalysed by choline (ethanolamine) kinase and phosphocholine (phosphoethanolamine) cytidylyltransferase are rate-limiting, whereas the phosphocholine (phosphoethanolamine) transferase step is near equilibrium in rat liver.

Animals↗

PubMed1976

Phospholipid synthesis in mammary tissue. Choline and ethanolamine kinases: kinetic evidence for two discrete active sites.

Choline and ethanolamine kinases are located in the high speed supernatant of lactating bovine mammary gland. Maximum activities of choline and ethanolamine kinases were observed at pH 9.2 and 8.0, respectively, with the rate of ethanolamine phosphorylation being 1/15 that of choline phosphorylation. Activation energies of 29 joules (Q10--1.5) and 31 joules (Q10 = 1.5) were calculated between 3.4 and 31.3 C for choline kinase and ethanolamine kinase, respectively. Above 31.3 C, the Arrhenius plot deviated from linearity for both enzymes, suggesting that denaturation was occurring. An apparent Km of 0.25 mM for choline was obtained for choline kinase activity. The apparent Km of ethanolamine kinase for ethanolamine was unusually high (17 mM), the activity was not linear with increasing protein concentration. Activity was tripled and the Km decreased to 2.5 mM when the enzyme preparation was washed with butanol: benzene mixture, suggesting the presence of an endogenous competitive inhibitor(s), with respect to ethanolamine. Choline kinase was not affected by the solvent wash. Substrate competition studies revealed that choline kinase was slightly inhibited competitively by ethanolamine (apparent Ki = 19-21 mM), whereas choline was a potent competitive inhibitor of ethanolamine kinase (apparent Ki = 0.33-0.50 mM). The results indicated that these two kinase activities were mediated by two distinct active sites, possibly on a single protein. The significance of choline in the regulation of phosphatidylethanolamine synthesis is discussed.

Animals↗