A novel multiple affinity purification tag and its use in identification of proteins associated with a cyclin-CDK complex

A novel multiple affinity purification (MAFT) or tandem affinity purification (TAP) tag has been constructed. It consists of the calmodulin binding peptide, six histidine residues, and three copies of the hemagglutinin epitope. This 'CHH' MAFT tag allows two or three consecutive purification steps, giving high purity. Active Clb2-Cdc28 kinase complex was purified from yeast cells after inserting the CHH tag into Clb2. Associated proteins were identified using mass spectrometry. These included the known associated proteins Cdc28, Sic1 and Cks1. Several other proteins were found including the 70 kDa chaperone, Ssa1.

Metabolism of benzo(a)pyrene by duck liver microsomes

The metabolism of benzo(a)pyrene [BP], a model carcinogenic PAH, by hepatic microsomes of two duck species, mallard (Anas platyrhynchos) and common merganser (Mergus merganser americanus) collected from chemically-contaminated and relatively non-contaminated areas was investigated. The rate of metabolism of BP by liver microsomes of common merganser and mallard collected from polluted areas (2,650 +/- 310 and 2,200 +/- 310 pmol/min per mg microsomal protein, respectively) was significantly higher than that obtained with liver microsomes of the two species collected from non-polluted areas (334 +/- 33 and 231 +/- 30 pmol/min per mg microsomal protein, respectively). The level of cytochrome P-450 1A1 was significantly higher in the liver microsomes of both duck species from the polluted areas as compared to the ducks from the non-polluted areas. The major BP metabolites, including BP-9, 10-diol, BP-4, 5-diol, BP-7, 8-diol, BP-1, 6-dione, BP-3, 6-dione, BP-6, 12-dione, 9-hydroxy-BP and 3-hydroxy-BP, formed by liver microsomes of both duck species from polluted and non-polluted areas, were qualitatively similar. However, the patterns of these metabolites were considerably different from each other. Liver microsomes of ducks from the polluted areas produced a higher proportion of benzo-ring dihydrodiols than the liver microsomes of ducks from the non-polluted areas, which converted a greater proportion of BP to BP-phenols. The predominant enantiomer of BP-7,8-diol formed by hepatic microsomes of the two duck species had an (-)R,R absolute stereochemistry. The data suggest that duck and rat liver microsomal enzymes have different regioselectivity but similar stereoselectivity in the metabolism of BP.

Purification and characterization of a low molecular weight zinc binding protein from human placenta

A low molecular weight, native zinc binding, cytosolic protein (LMZP) has been isolated, purified and characterized from human normal term placenta. Gel filtration of heat treated placental cytosol after sequential acetone precipitation (80% ppt) revealed a major zinc binding protein in the range of low molecular weight. This partially purified zinc binding fraction was further fractionated on DEAE-Sephadex A-25. The zinc was eluted in one of the three peak fractions. Further, the purity of zinc binding protein was confirmed on fast protein liquid chromatography (FPLC). The purified placental LMZP was homogenous on SDS-polyacrylamide gel electrophoresis with a single band. Ultraviolet (UV) spectrum of LMZP showed an absorption maximum at 257 nm which disappeared at pH 2. Molecular weight of LMZP as determined by gel chromatography, SDS-polyacrylamide gel electrophoresis and amino acid analysis was 6 kDa. It was calculated that 1 g atom of zinc was bound to 1 mole of the LMZP. Unlike in classical metallothionein, the amino acid composition of placental LMZP revealed the presence of aromatic amino acids, lower content of cysteine and higher content of histidine, glutamic acid and aspartic acid (10, 9 and 5 residues/mole, respectively).