Recently Zhang et al. cloned a gene that is expressed only in adipose tissue of the mouse. The obese phenotype of the ob/ob mouse is linked to a mutation in the obese gene that results in expression of a truncated inactive protein. Human and rat homologues for this gene are known. Previous experiments predict such a hormone to have a hypothalamic target. Hypothalamic neuropeptide Y stimulates food intake, decreases thermogenesis, and increases plasma insulin and corticosterone levels making it a potential target. Here we express the obese protein in Escherichia coli and find that it suppresses food intake and decreases body weight dramatically when administered to normal and ob/ob mice but not db/db (diabetic) mice, which are thought to lack the appropriate receptor. High-affinity binding was detected in the rat hypothalamus. One mechanism by which this protein regulated food intake and metabolism was inhibition of neuropeptide-Y synthesis and release.

The deposition of the ␤ amyloid peptide in neuritic plaques and cerebral blood vessels is a hallmark of Alzheimer's disease (AD) pathology. The major component of the amyloid deposit is a 4.2-kDa polypeptide termed amyloid ␤-protein of 39 -43 residues, which is derived from processing of a larger amyloid precursor protein (APP). It is hypothesized that a chymotrypsin-like enzyme is involved in the processing of APP.We have discovered a new serine protease from the AD brain by polymerase chain reaction amplification of DNA sequences representing active site homologous regions of chymotrypsin-like enzymes. A cDNA clone was identified as one out of one million that encodes Zyme, a serine protease. Messenger RNA encoding Zyme can be detected in some mammalian species but not in mice, rats, or hamster. Zyme is expressed predominantly in brain, kidney, and salivary gland. Zyme mRNA cannot be detected in fetal brain but is seen in adult brain. The Zyme gene maps to chromosome 19q13.3, a region which shows genetic linkage with late onset familial Alzheimer's disease.When Zyme cDNA is co-expressed with the APP cDNA in 293 (human embryonic kidney) cells, amyloidogenic fragments are detected using C-terminal antibody to APP. These co-transfected cells release an abundance of truncated amyloid ␤-protein peptide and shows a reduction of residues 17-42 of A␤ (P3) peptide. Zyme is immunolocalized to perivascular cells in monkey cortex and the AD brain. In addition, Zyme is localized to microglial cells in our AD brain sample. The amyloidogenic potential and localization in brain may indicate a role for this protease in amyloid precursor processing and AD.The generation of the ␤ amyloid peptide is thought to be the result of processing of the amyloid precursor protein (APP) 1 by one or more proteases. After the deduced amino acid sequence of APP was revealed, a number of laboratories initiated studies to purify and characterize the N-terminal cleaving enzyme of amyloid ␤-protein (A␤), termed ␤-secretase (1). The cleavage of the Met 596 -Asp 597 bond of the full-length APP generates the N-terminal amino acid of A␤, which was first shown by Glenner and Wong (2) to be aspartic acid. ␤-Secretase is yet an unidentified protease.Several themes and strategies influenced the direction of investigation of ␤-secretase. The first strategy was to follow a traditional biochemical purification. Assays were utilized in which short peptide substrates were substituted for the large transmembrane precursor protein (1). Any enzyme capable of making a methionine (M)/aspartic acid (D) cleavage could be designated a potential ␤-secretase. The second theme, since the amino acid that surrounded the N terminus of A␤ was found to be a methionine, was some laboratories have rationalized that a search for an enzyme with chymotrypsin-like specificity (a specificity for cleavage of subtrates containing a neutral hydrophobic residue at the S1 subsite) was necessary (3-7).To facilitate the second approach, we have developed a method to identify chymotrypsin-l...

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