Journal of Lipid Research, Vol. 12, 324-330, May 1971
Copyright © 1971 by Lipid Research, Inc.
Interaction of beef liver lipase with mixed micelles of tripalmitin and Triton X-100
Arnold Kaplan and Mei-Hui Teng
Department of Microbiology, Saint Louis University Medical School, Saint Louis, Missouri 63104
When concentrated dispersions of tripalmitin in Triton X-100 are added to reaction mixtures containing soluble beef liver lipase, the rate of hydrolysis of tripalmitin increases with incubation time. When the diluted substrate is aged at 37°C for 3 hr before the addition of enzyme, the rate of hydrolysis is greater than the rate with freshly diluted dispersions and is constant for at least 2 hr. The reciprocal of the rate of hydrolysis is a complex function of the reciprocal of the substrate concentration when measured with freshly diluted substrate dispersions. A linear relationship between these reciprocals is obtained when measured with aged preparations of substrate. The rate and extent of increase of the velocity of hydrolysis of the aged substrate in relation to the velocity of hydrolysis of freshly diluted substrate are directly proportional to the substrate concentration and inversely proportional to the Triton X-100 concentration. The apparent Vmax of beef liver lipase for tripalmitin in diluted and aged dispersions is independent of the Triton X-100 concentration, while the apparent Km is inversely proportional to the Triton X-100 concentration. The apparent Km for tripalmitin complexes at zero Triton X-100 concentration was judged to be 7.5 x 10-5 m. The molecular size of dispersion complexes does not change significantly as dispersions are aged. The spherical diameter of the complexes assessed by gel filtration techniques is in the order of 100 A.
Supplementary key words kinetics • glycerol tripalmitate-1-14C
Submitted on July 24, 1970
Accepted on January 14, 1971
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