Identification of the adipocyte acid phosphatase as a PAO-sensitive tyrosyl phosphatase.

We have partially purified an 18-kDa cytoplasmic protein from 3T3-L1 cells, which dephosphorylates pNPP and the phosphorylated adipocyte lipid binding protein (ALBP), and have identified it by virtue of kinetic and immunological criteria as an acid phosphatase (EC 3.1.3.2). The cytoplasmic acid phosphatase was inactivated by phenylarsine oxide (PAO) (Kinact = 10 microM), and the inactivation could be reversed by the dithiol, 2,3-dimercaptopropanol (Kreact = 23 microM), but not the monothiol, 2-mercaptoethanol. Cloning of the human adipocyte acid phosphatase revealed that two isoforms exist, termed HAAP alpha and HAAP beta (human adipocyte acid phosphatase), which are distinguished by a 34-amino acid isoform-specific domain. Sequence analysis shows HAAP alpha and HAAP beta share 74% and 90% identity with the bovine liver acid phosphatase, respectively, and 99% identity with both isoenzymes of the human red cell acid phosphatase but no sequence similarity to the protein tyrosine phosphatases (EC 3.1.3.48). HAAP beta has been cloned into Escherichia coli, expressed, and purified as a glutathione S-transferase fusion protein. Recombinant HAAP beta was shown to dephosphorylate pNPP and phosphoALBP and to be inactivated by PAO and inhibited by vanadate (Ki = 17 microM). These results describe the adipocyte acid phosphatase as a cytoplasmic enzyme containing conformationally vicinal cysteine residues with properties that suggest it may dephosphorylate tyrosyl phosphorylated cellular proteins.     

Isolation and characterization of porcine somatotropin containing a succinimide residue in place of aspartate129.

Aspartate129 in porcine somatotropin was converted into a cyclic imide residue (succinimide) under acidic solution conditions. Reversed-phase high performance liquid chromatography was utilized to isolate and quantitate this altered species, which accounted for approximately 30% of the total protein. The molecular mass of this modified species was determined by electrospray mass spectrometry to be 18 Da less than normal porcine somatotropin, indicative of a loss of 1 H2O molecule. Tryptic peptide mapping demonstrated that the peptide composed of residues 126-133 was altered in this modified protein. Amino acid analysis, amino acid sequencing, mass spectrometry, and capillary zone electrophoresis were used to demonstrate that aspartate129 in this peptide had been converted into a succinimide residue. Further confirmation that this peptide contained a succinimide was obtained by hydrolyzing the modified peptide at pH 9.0, which yielded both the aspartate and isoaspartate peptides.     

Apoptosis: final control point in cell biology

The discovery of apoptosis, a widespread and morphologically distinct form of physiological cell death, has had an extraordinary impact on cell biology. The importance of apoptosis stems from its active nature and its potential for controlling biological systems. The growing appreciation of the significance of this process has stimulated intense investigation into the molecular mechanisms involved and into its fundamental implications for developmental biology, immunology and oncology.     

Structure of equine corticotropin releasing factor

A 41 amino acid peptide, probably identical in structure to human corticotropin releasing factor, was isolated from 70 equine hypothalami by methanol extraction, immunoaffinity chromatography and single step of reverse phase HPLC. The amino acid sequence was determined by gas phase sequence analysis. Probable carboxyl terminal amidation was demonstrated by similar retention times for equine and human corticotropin releasing factor on reverse phase HPLC at pH 8. The likely structure of equine corticotropin releasing factor is: Ser-Glu-Glu-Pro-Pro- Ile-Ser-Leu-Asp-Leu-Thr-Phe-His-Leu-Leu-Arg-Glu-Val-Leu-Glu-Met-Ala-Arg-Ala-Glu-Gln-Leu-Ala-Gln-Gln-Ala-His-Ser-Asn- Arg-Lys-Leu-Met-Glu-Ile-Ile-NH₂. The purified peptide is equipotent with human corticotropin releasing factor in an in vitro bioassay and in a human plasma binding protein assay.     

Glucose transport throughout fermentation by Saccharomyces cerevisiae NCYC 1108

The rate of fermentation of glucose by a polyploid strain of Saccharomyces cerevisiae growing in a defined salts medium depends on the availability of NH₄+⁺. Its decline after exhaustion of the nitrogen source corresponded with the ability of the cells to accumulate the glucose analogue 2-deoxyglucose. Addition of NH₄+⁺to a nitrogen-depleted culture stimulated both glucose utilization and 2-deoxyglucose uptake. Since stimulation was inhibited by cycloheximide, maintenance of glucose transport during fermentation is dependent on protein synthesis.     

Prohibitin, an evolutionarily conserved intracellular protein that blocks DNA synthesis in normal fibroblasts and HeLa cells.

Genes that act inside the cell to negatively regulate proliferation are of great interest because of their implications for such processes as development and cancer, but these genes have been difficult to clone. This report details the cloning and analysis of cDNA for prohibitin, a novel mammalian antiproliferative protein. Microinjection of synthetic prohibitin mRNA blocks entry into S phase in both normal fibroblasts and HeLa cells. Microinjection of an antisense oligonucleotide stimulates entry into S phase. By sequence comparison, the prohibitin gene appears to be the mammalian analog of Cc, a Drosophila gene that is vital for normal development.