A B S T R A C T The addition of apoprotein E isolated from human very low density lipoproteins to both rat lymph chylomicrons and a triglyceride emulsion significantly increased the hepatic uptake of these particles in a nonrecycling isolated rat liver perftision system. The cleared triglyceride was removed without apparent hydrolysis by the hepatocyte. When lymph chylomicrons were loaded with both Apo E and Apo C proteins by exposture to rat plasma, no increment in hepatic clearance was observed. Sequential evaluations of the influence of the C apoproteins on the hepatic clearance of both emulsions an(l chylomicrons revealed that the CIII (CIII-1) protein had a pronounced inhibitory effect on hepatic removal. The inhibition was observed for both Apo E-enriched chylomicrons and those containing little of this apoprotein.

A B S T R A C T An arginine-rich apoprotein obtained from human triglyceride-rich lipoprotein was isolated on a heparin affinity column when either the aqueousor urea-soluble apoproteins were applied to the column. Of all the aqueous-or urea-soluble apoproteins, only this arginine-rich protein exhibited a binding affinity to heparin. This protein was eluted from the column at sodium chloride concentrations above 0.35 M in the absence of urea and between 0.17-0.2 M when isolated in urea. The protein has been characterized by amino acid analysis, immunoelectrophoresis, dodecyl sulfate polyacrylamide electrophoresis, isoelectric focusing, and NH2-terminal analysis. It has the same amino acid composition, NH2-terminal, and molecular weight as previously described for human argininerich apoprotein.The triglyceride-rich lipoproteins of fasting normal humans were eluted as two fractions when applied to the heparin affinity column. A small amount was eluted in the unbound fraction and this species contained virtually no arginine-rich apoprotein. The bulk of the triglyceride-rich lipoproteins eluted in the bound fraction and contained appreciable amounts of argininerich apoprotein. The bound lipoproteins had more cholesterol and cholesterol ester and less triglyceride than the unbound. The isolated arginine-rich apoprotein was derivatized with phenylglyoxal with a resulting alteration of 75% of the arginine residues. This modified apoprotein did not bind to the heparin affinity column. Similar treatment of the whole triglyceriderich lipoprotein produced a lipoprotein that was totally eluted in the unbound fraction.

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and 92 % by 1 mM-stearate and 1 mM-oleate respectively. 9. The results are discussed in relation to the general problems of isolating 'intact' plant mitochondria and the action of fatty acids in inhibiting mitochondrial functions. The authors are indebted to Dr F. D. Collins for valuable discussions. L.D. held a Sir John and Lady Higgins Research Scholarship from the University of Melbourne during this work. The Pye Chromatograph was used by courtesy of F. V. Harold and A. S. Morieson, of Carlton and United Breweries.