Michael F. Rohde

Action of lecithin:Cholesterol acyltransferase on model lipoproteins: Preparation and characterization of model nascent high density lipoprotein

Apolipoprotein A-I, the major protein of human plasma high density lipoprotein, is the primary activator of plasma lecithin:cholesterol acyltransferase. In vitro, the association of apolipoprotein A-I with physiological phosphatidylcholines can be catalyzed by mixing the protein and lipid with sodium cholate, which is removed by chromatography. The apolipoprotein A-I/phospholipid complex has the physical properties of an HDL, and when cholesterol is present the complex is a highly reactive substrate in the lecithin:cholesterol acyltransferase-catalyzed reaction. The relative reactivity of this complex compared with a number of other lipid-protein complexes is presented and discussed.

The cyanogen bromide peptides of the apoprotein of low density lipoprotein (apoB): Its molecular weight from a chemical view

Abstract After >95% cleavage of the apoprotein (apoB) of the low density lipoproteins with cyanogen bromide, the peptides produced are shown to be extensively aggregated in sodium dodecyl sulfate. Both high temperature and increased concentration (5%) of the detergent are necessary to shift the aggregated peptides from high molecular weight (>25,000) to lower molecular weight aggregates as seen on sodium dodecyl sulfate polyacrylamide gel electrophoresis. End group analyses of the cyanogen bromide digestion by automated sequencer techniques indicate the presence of five (5) methionines. With a known methionine content of 16 moles/100,000 g protein, the molecular weight of the apoprotein must be approximately 30,000.

Lipoprotein-apoprotein exchange in aqueous systems: Relevance to the occurrence of APOA-I and APOC proteins in a common particle

Summary Human plasma high density lipoproteins (HDL) were labeled in vitro with [ 125 I]apoA-I. Chromatography of the [ 125 I]HDL on Sephacryl S-200 revealed that a certain fraction of [ 125 I]apoA-I readily dissociates from the intact particle over a wide range of HDL concentrations. The relatively constant value of the dissociated apoA-I concentration observed at various HDL concentrations suggests that a “critical monomer concentration” of apoA-I is in equilibrium with the parent lipoprotein. Addition of [ 131 I]apoC proteins to HDL induces additional dissociation of oligomeric apoA-I with the concomitant incorporation of apoC into a new particle of about 460,000 daltons.

Resolution of components in sedimentation equilibrium concentration distributions.

Abstract A procedure is discussed whereby the concentration distribution at sedimentation equilibrium may be resolved into the contributing redistributed components in the system. The procedure is shown to deal best with heterogeneous systems, but can also lend itself to the analysis of a system where the molecular weights of interacting proteins are quite similar by making composition constraints. In those cases where interaction occurs between components of the system, a calculation of the equilibrium constant which described the association can be made. Moreover, the fitting error is related to the fitting parameters in such a manner as to yield the estimated error of the equilibrium constant.