Tweens as a Substrate for Determination of the Clearing Factor

¹ From the Department of Gastro-Intestinal Research, Medical Research Institute of Michael Reese Hospital, and the Department of Medicine, The University of Chicago, Chicago, Illinois, and Hospital B. Churruca, Buenos Aires, Argentina

A quantitative method is proposed for the determination of the clearing factor in serum, using Tween 60 as a substrate. The degree of turbidity produced by the combination of the liberated fatty acids with calcium chloride is expressed in terms of micromoles of calcium laurate. The substrate is not hydrolyzed by normal human or dog's serum. Small amounts of serum are necessary for the reaction, the substrate is easily prepared and the results are reproducible. Extracts of human liver and pancreas showed relatively low activity towards the substrate. Liver and pancreas esterases and postheparin serum showed specific, distinctly different inhibition patterns in the presence of various drugs, such as sodium lauryl sulfate, eserine salicylate, DFP, E 6000, heparin, magnesium and sodium and potassium chloride.