Alkaline phosphatase conjugated protein A as a sensitive reagent to immunoscreen an expression cDNA plasmid library: isolation of cDNA to the calcium-binding protein of the chick embryonic chorioallantoic membrane

Mouse placental 57-kDa calcium-binding protein: I. Cloning of cDNA and characterization of developmental expression

A cDNA clone to the mouse placental 57-kDa calcium-binding protein (MCaBP) [29] was isolated by immunoscreening a mouse placenta cDNA library constructed in the expression phage vector, lambda gt 11. The MCaBP cDNA was 0.7 kb in size, with restriction sites for StuI and Bg/II, and its identity to the MCaBP was confirmed by mRNA hybrid selection. RNA blot hybridization revealed a predominant, 3.9-kb transcript of the MCaBP in day-18 mouse placenta. The expression of the MCaBP during development was analyzed with respect to the levels of protein activity, translatable MCaBP mRNA, and total MCaBP transcript.

Rat hepatic glutaminase: purification and immunochemical characterization

A method for the purification of phosphate-activated glutaminase from the liver of streptozotocin-diabetic rats is described. The procedure involves solubilization of glutaminase activity from isolated mitochondria by sonication, followed by ammonium sulfate precipitation, polyethylene glycol precipitation, and sequential chromatography on DEAE, hydroxylapatite, and zinc-chelated resins. The enzyme was purified 600-fold to a specific activity of 31-57 U/mg protein. The purified enzyme has an apparent subunit molecular mass of 58,000-Da and is greater than 80% pure by scanning densitometry of sodium dodecyl sulfate-polyacrylamide gels. The purified enzyme has an apparent Km for glutamine of 17 mM and a pH optimum between 7.8 and 8.2. The physical and kinetic properties of this enzyme are similar to those of the enzyme from normal rat liver. Polyclonal antibodies raised against the enzyme specifically inhibit hepatic glutaminase activity and react primarily with a 58,000-Da peptide in liver fractions on immunoblots. These antibodies were used in equivalence point titrations and immunoblots to provide evidence for increased concentration of glutaminase protein in the liver of diabetic rats with no change in specific activity of the enzyme. In addition, the antibodies cross-react, at low affinity, with kidney-type glutaminases. On immunoblots, the antibodies did not react with fetal liver, mammary gland, or lung. Antibodies to rat hepatic glutaminase should prove useful as tools to study the long-term regulation of the enzyme.