The penetration of serum albumin into phospholipid monolayers of different fatty acid chain length and interfacial charge.
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ABSTRACT:
SUBMITTER: Quinn P
PROVIDER: S-EPMC1179313 | biostudies-other | 1970 Aug
REPOSITORIES: biostudies-other
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Project description:Phospholipids are found throughout the natural world, including the lung surfactant (LS) layer that reduces pulmonary surface tension and enables breathing. Fibrinogen, a protein involved in the blood clotting process, is implicated in LS inactivation and the progression of disorders such as acute respiratory distress syndrome. However, the interaction between fibrinogen and LS at the air-water interface is poorly understood. Through a combined microrheological, confocal and epifluorescence microscopy approach we quantify the interfacial shear response and directly image the morphological evolution when a model LS monolayer is penetrated by fibrinogen. When injected into the subphase beneath a monolayer of the phospholipid dipalmitoylphosphatidylcholine (DPPC, the majority component of LS), fibrinogen preferentially penetrates disordered liquid expanded (LE) regions and accumulates on the boundaries between LE DPPC and liquid condensed (LC) DPPC domains. Thus, fibrinogen is line active. Aggregates grow from the LC domain boundaries, ultimately forming a percolating network. This network stiffens the interface compared to pure DPPC and imparts the penetrated monolayer with a viscoelastic character reminiscent of a weak gel. When the DPPC monolayer is initially compressed beyond LE-LC coexistence, stiffening is significantly more modest and the penetrated monolayer retains a viscous-dominated, DPPC-like character.
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Project description:The kinetics of the interaction of long-chain fatty acids (referred to as fatty acids) with albumin is critical to understanding the role of albumin in fatty acid transport. In this study we have determined the kinetics of fatty acid dissociation from BSA and the BSA-related fatty acid probe BSA-HCA (BSA labelled with 7-hydroxycoumarin-4-acetic acid) by stopped-flow methods. Fatty acid-albumin complexes of a range of natural fatty acid types and albumin molecules (donors) were mixed with three fatty acid-binding acceptor proteins. Dissociation of fatty acids from the donor was monitored by either the time course of donor fluorescence/absorbance or the time course of acceptor fluorescence. The results of these measurements indicate that fatty acid dissociation from BSA as well as BSA-HCA is well described by a single exponential function over the entire range of fatty acid/albumin molar ratios used in these measurements, from 0.5:1 to 6:1. The observed rate constants (k(obs)) for the dissociation of each fatty acid type reveal little or no dependence on the initial fatty acid/albumin ratio. However, dissociation rates were dependent upon the type of fatty acid. In the case of native BSA with an initial fatty acid/BSA molar ratio of 3:1, the order of k(obs) values was stearic acid (1.5 s(-1)) < oleic acid < palmitic acid congruent with linoleic acid<arachidonic acid (8 s(-1)) at 37 degrees C. The corresponding values for BSA-HCA were about half the values for BSA. The results of this study show that the rate of fatty acid dissociation from native BSA is more than 10-fold faster than reported previously and that the off-rate constants for the five primary fatty acid-binding sites differ by less than a factor of 2. We conclude that for reported rates of fatty acid transport across cell membranes, dissociation of fatty acids from the fatty acid-BSA complexes used in the transport studies should not be rate-limiting.
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Project description:The interaction of long-chain fatty acids with cells is important for their uptake and metabolism, as well as their involvement in signalling processes. The majority of long-chain fatty acids circulating in plasma exist as complexes with serum albumin. Thus an understanding of the involvement of serum albumin in these processes is vitally important. The effect of serum albumin on the uptake of long-chain fatty acids was studied in 3T3-L1 adipocytes. Serum albumin had a stimulatory effect on oleate uptake at all ratios of oleate: serum albumin tested. Furthermore, the rate of oleate uptake was saturable with increasing concentrations of serum albumin when the oleate: serum albumin ratio, and therefore the concentration of uncomplexed oleate, remained constant. This was not due to uptake being limited by dissociation of oleate from serum albumin, because oleate did not appear to be limiting. Furthermore, at very high ratios of oleate: serum albumin, when the concentration of uncomplexed oleate was predicted to be large relative to the amount of oleate taken up by cells, the rate of oleate uptake was still dependent on the albumin concentration. Serum albumin, covalently labelled with the photoreactive fatty acid 11-m-diazirinophenoxy[11-3H]undecanoate, bound to cells in a manner exhibiting both saturable (Kd 66.7 microM) and non-saturable processes. These results indicate that the stimulatory effect of serum albumin on the rate of oleate uptake is due to a direct interaction of serum albumin with the cells and point to an involvement of albumin binding sites in the cell surface in the cellular uptake of long-chain fatty acids.
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Project description:The kinetics of the Ca(2+)-ATPase purified from sarcoplasmic reticulum have been studied after reconstitution into bilayers of dimyristoleoylphosphatidylcholine [di(C14:1)PC], dioleoylphosphatidylcholine[di(C18:1)PC] and dinervonylphosphatidylcholine [di(C24:1)PC]. In di(C24:1)PC the rate of phosphorylation of the ATPase by ATP was comparable with that in di(C18:1)PC (about 70 s-1), but in di(C14:1)PC the rate was much lower (21 s-1). Fluorescence responses of the ATPase suggest changes in the phosphoryl-transfer step rather than in the preceding conformational change E1Ca2ATP<-->E1'Ca2ATP. The rate of dephosphorylation of the phosphorylated ATPase was found to decrease in the order di(C24:1)PC < di(C14:1)PC < di(C18:1)PC. For the ATPase in di(C24:1)PC the rate of dephosphorylation (3.3 s-1) was slow enough to be the rate-limiting step for ATP hydrolysis; in di(C14:1)PC, it is suggested that both phosphorylation and dephosphorylation contribute to rate limitation. Phosphorylation of the ATPase in di(C24:1)PC by Pi was normal, but no phosphoenzyme could be detected in di(C14:1)PC. The rate of the Ca(2+)-transport step was normal in di(C24:1)PC, suggesting that the single Ca2+ ion bound to the ATPase in di(C24:1)PC could be transported.
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