Consideration of the kinetics of the evaporation of peptides leads to two approaches to volatility enhancement. An obvious direction to take is to attempt to reduce the energy of bonding of molecules to surfaces by dispersal onto surfaces which are relatively inert.
SUMMARY The concentrations of angiotensin converting enzyme (ACE) activity, norepinephrine, and serotonin were measured in microdissected regions of the dog's brainstem and spinal cord. In addition, we determined the in vitro metabolism of 125 I-angiotensin I (Ang I) hi hompgenates of the same brain pnnch regions. High ACE-specific activity was found hi the monoamine-containing regions of the brainstem and in the intermediolateral column of the spinal cord. In brainstem homogenates '"I-Ang I was metabolized to angiotensin II (Ang- [l-8]) and the N-terminal heptapeptide Ang-(l-7). In the presence of MK 422 (50 fiM), Ang-(l-7) was still generated, while the production of Ang-(l-8) was inhibited. This study revealed the presence of high ACE activity in monoamine regions of dog brainstem and spinal cord, and showed that the metabolite Ang-(l-7) is the major product generated from Ang I in the presence and absence of ACE inhibition. (Ang H) in the central nervous system is limited by our lack of knowledge of the functional neurochemistry of the brain reninangiotensin system (RAS) in regions that may produce the peptide for actions on neuronal circuits engaged in autonomic function.12 Because catecholamine neuronal groups of the dorsal and ventral brainstem and the spinal cord have a major role in blood pressure regulation and the evolution of some forms of experimental hypertension, 3 we determined the distribution of the angiotensin converting enzyme (ACE) in these areas in the dog. We studied also the proteolytic hydrolysis of angiotensin I (Ang I) in brain punch homogenates obtained from these regions to evaluate the biochemical pathways that account for the generation and metabolism of angiotensins in the brain.
SUMMARYThe most sensitive nonradiometric routine assay for angiotensin-converting enzyme (ACE) activity uses fluorometry to detect His-Leu released from Hip-His-Leu. Our results indicate that, in contrast to human serum, rat serum and plasma contain large and variable amounts of dipeptidase activity that lead to a subestimation of the ACE activity measured in 0.1 M potassium phosphate buffer, pH 8.3, containing 0.3 M NaCI, the most commonly used assay for human serum and tissue ACE. We describe and validate an assay for 1 to 10 /xL rat and human serum or plasma using 5 mM Hip-His-Leu in 500 fiL of 0.4 M sodium borate buffer, pH 8.3, containing 0.9 M NaCI at 37°C that reduced the subestimation error to ^ 3% (rat serum) and ^ 0.1% (human serum) and increased the ACE activity twofold to threefold. The K m and V,^ are reported for rat serum ACE
Host cell invasion by Toxoplasma gondii is a multistep process with one of the first steps being the apical release of micronemal proteins that interact with host receptors. We demonstrate here that micronemal protein 1 (MIC1) is a lactose-binding lectin. MIC1 and MIC4 were recovered in the lactose-eluted (Lac(+)) fraction on affinity chromatography on immobilized lactose of the soluble antigen fraction from tachyzoites of the virulent RH strain. MIC1 and MIC4 were both identified by N-terminal microsequencing. MIC4 was also identified by sequencing cDNA clones isolated from an expression library following screening with mouse polyclonal anti-60/70 kDa (Lac(+) proteins) serum. This antiserum localized the Lac(+) proteins on the apical region of T. gondii tachyzoites by confocal microscopy. The Lac(+) fraction induced hemagglutination (mainly type A human erythrocytes), which was inhibited by beta-galactosides (3 mM lactose and 12 mM galactose) but not by up to 100 mM melibiose (alpha-galactoside), fucose, mannose, or glucose or 0.2 mg/ml heparin. The lectin activity of the Lac(+) preparation was attributed to MIC1, because blotted MIC1, but not native MIC4, bound human erythrocyte type A and fetuin. The copurification of MIC1 and MIC4 may have been due to their association, as reported by others. These data suggest that MIC1 may act through its lectin activity during T. gondii infection.
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