ABSTRACT
We have modified the 63Ni radiochemical method of Ho (Anal Biochem 1970;36:105) for determination of free fatty acids (FFA) in plasma. Extracting 1 or 0.1 mL of plasma with Dole's mixture (J Biol Chem 1960;235:2595) and washing the "heptane" layer with two volumes of isopropanol/water/dilute (0.5 mol/L) H2SO4 (25/25/1, by vol) removes about 90% of the lipid phosphorus from the "heptane" layer without removing any FFA and is more convenient than treatment with silicic acid. The following modifications decrease background radioactivity and improve separation of the organic phase from the water phase containing the uncomplexed 63Ni: (a) use glassware instead of plastic test tubes; (b) evaporate the organic phase to dryness before adding the 63Ni (this removes the isopropanol, which interferes with the 63Ni assay); and (c) add anhydrous sodium sulfate before the final centrifugation step.
Subject(s)
Fatty Acids, Nonesterified/blood , Nickel , Radioisotopes , Fatty Acids, Nonesterified/isolation & purification , Humans , Indicators and Reagents , Phospholipids/isolation & purification , Quality Control , Radiochemistry , Scintillation Counting , Silicic Acid , Solutions , SulfatesABSTRACT
The protease activity in guts of Ornithodoros tholozani females was studied in vitro. The intracellular protease in Ornithodoros tholozani guts has a pH optimum of about 3.0. Hemoglobin is the preferred substrate, and bovine serum albumin is digested very slowly. In this respect the protease resembles cathepsin D. Unfed ticks contain a small amount of protease in the gut. After feeding the level of protease increases gradually for several days until peak protease activity is attained. The level of gut protease activity depends on the size of the blood meal taken and on the interval after feeding. After a period of peak protease activity, the level of protease declines. The level of gut protease in unmated females (kept at 27 degrees C) did not reach prefeeding levels within 100 days. The level of gut proteolytic activity, as determined by in vitro protease assays, does not reflect the degree of blood digestion which takes place in vivo. After a period of rapid digestion, lasting for about two weeks, the undigested part of the blood meal remains unchanged in the lumen of the gut. At that time the gut tissue contains considerable levels of protease, which can be demonstrated by in vitro assays. Presumably, the protease remains active inside the gut cells, although the uptake of hemoglobin from the gut lumen has ceased. The results are compared to those obtained in other tick species.
