Topo-dynamic characteristics of human plasma VLDL apolipoproteins and efficiency of triacylglycerol hydrolysis by lipoprotein lipase.
A lower accessibility to water-soluble quenchers of tryptophanyls of VLDL apolipoproteins B, E, C as compared to LDL apoB chromophores has been detected by a fluorescence quenching technique. The dynamic behaviour of the tryptophanyls of VLDL amphipathic apolipoproteins E and C did not change in the presence of a detergent, Tween-20, at sub-lytic concentrations. However, a reversible structural transition registered by the 'red' shift of the emission spectrum maximum and the changes in the quenching pattern by I- occurred under these conditions. The increase in the VLDL tryptophanyl accessibility to acrylamide and the decrease in the quenching constant were observed at partial and complete solubilization of the VLDL particles by the detergent. Dissociation of apolipoproteins from VLDL occurred after their treatment with Tween-20 or lipoprotein lipase isolated from bovine milk, and the tryptophanyl population not participating in fluorescence energy transfer on lipid phase-localized fluorescent probe pyrene appeared. In the presence of Tween-20, the relative affinity of apoE for the lipid matrix of VLDL was lower than that of apoC. Besides, the uncompetitive mode of inhibition of the LPL activity by apoC-III has been demonstrated. It is suggested that: (1) the amphipathic apolipoproteins E and C are organized as clusters on the VLDL surface and/or partially shielded by apolipoprotein B: (2) self-regulation of lypolysis may exist involving detergent-like reaction product accumulation and changes in relative apolipoprotein contents.
Biochemistry Department, USSR Research Centre for Preventive Medicine, Moscow.
A D
AD
Dergunov
V V
VV
Shuvaev
N V
NV
Perova
D000818:Animals; D001055:Apolipoproteins B / Q000097:blood*; D001056:Apolipoproteins C / Q000097:blood*; D001057:Apolipoproteins E / Q000097:blood*; D002417:Cattle; D003840:Deoxycholic Acid / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008071:Lipoprotein Lipase / Q000097:blood* / Q000378:metabolism; D008079:Lipoproteins, VLDL / Q000097:blood; D008892:Milk / Q000201:enzymology; D011136:Polysorbates / Q000494:pharmacology; D011487:Protein Conformation; D014280:Triglycerides / Q000378:metabolism; D014364:Tryptophan
D001055:Apolipoproteins B; D001056:Apolipoproteins C; D001057:Apolipoproteins E; D008079:Lipoproteins, VLDL; D011136:Polysorbates; D014280:Triglycerides; D003840:Deoxycholic Acid; D014364:Tryptophan; D008071:Lipoprotein Lipase