Physiology: does gut hormone PYY3-36 decrease food intake in rodents?

Batterham et al. report that the gut peptide hormone PYY3-36 decreases food intake and body-weight gain in rodents, a discovery that has been heralded as potentially offering a new therapy for obesity. However, we have been unable to replicate their results. Although the reasons for this discrepancy remain undetermined, an effective anti-obesity drug ultimately must produce its effects across a range of situations. The fact that the findings of Batterham et al. cannot easily be replicated calls into question the potential value of an anti-obesity approach that is based on administration of PYY3-36.     

Influence of castration and testosterone replacement on hypothalamic tyrosine hydroxylase activity in the rat.

Hypothalamic tyrosine hydroxylase (TH) activity of castrate rats is modulated by testosterone propionate (TP) in vivo. Kinetic studies revealed that both Vmax and Km were virtually unaltered for substrate tyrosine in the presence of an excess of DMPH4 cofactor. TP replacement to castrate rats increased the Km for added DMPH4 cofactor, while Vmax decreased. These results suggest that TP decreases TH activity of castrate rats by inhibiting the enzyme-reduced pteridine cofactor complex.     

Influence of castration and testosterone replacement on hypothalamic tyrosine hydroxylase activity in the rat

Summary Hypothalamic tyrosine hydroxylase (TH) activity of castrate rats is modulated by testosterone propionate (TP) in vivo. Kinetic studies revealed that bothV _max andK _m were virtually unaltered for substrate tyrosine in the presence of an excess of DMPH₄ cofactor. TP replacement to castrate rats increased theK _m for added DMPH₄ cofactor, whileV _max decreased. These results suggest that TP decreases TH activity of castrate rats by inhibiting the enzymereduced pteridine cofactor complex.     

The secreted form of the Alzheimer's amyloid precursor protein with the Kunitz domain is protease nexin-II

The A4 protein (or beta-protein) is a 42- or 43-amino-acid peptide present in the extracellular neuritic plaques in Alzheimer's disease and is derived from a membrane-bound amyloid protein precursor (APP). Three forms of APP have been described and are referred to as APP695, APP751 and APP770, reflecting the number of amino acids encoded for by their respective complementary DNAs. The two larger APPs contain a 57-amino-acid insert with striking homology to the Kunitz family of protease inhibitors. Here we report that the deduced amino-terminal sequence of APP is identical to the sequence of a cell-secreted protease inhibitor, protease nexin-II (PN-II). To confirm this finding, APP751 and APP695 cDNAs were over-expressed in the human 293 cell line, and the secreted N-terminal extracellular domains of these APPs were purified to near homogeneity from the tissue-culture medium. The relative molecular mass and high-affinity binding to dextran sulphate of secreted APP751 were consistent with that of PN-II. Functionally, secreted APP751 formed stable, non-covalent, inhibitory complexes with trypsin. Secreted APP695 did not form complexes with trypsin. We conclude that the secreted form of APP with the Kunitz protease inhibitor domain is PN-II.     

Solid-phase gene assembly

New technologies for multiple chemical synthesis of oligonucleotides and stepwise hybridization on a solid-phase support enable the rapid and cost-effective preparation of long duplex DNA regions. Will these new technologies usher in a new era in protein engineering?