1
|
Liu L, Zou Y, Bhattacharya A, Zhang D, Lang SQ, Houk KN, Devaraj NK. Enzyme-free synthesis of natural phospholipids in water. Nat Chem 2020; 12:1029-1034. [PMID: 33046841 DOI: 10.1038/s41557-020-00559-0] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Accepted: 08/25/2020] [Indexed: 11/09/2022]
Abstract
All living organisms synthesize phospholipids as the primary constituent of their cell membranes. Enzymatic synthesis of diacylphospholipids requires preexisting membrane-embedded enzymes. This limitation has led to models of early life in which the first cells used simpler types of membrane building blocks and has hampered integration of phospholipid synthesis into artificial cells. Here we demonstrate an enzyme-free synthesis of natural diacylphospholipids by transacylation in water, which is enabled by a combination of ion pairing and self-assembly between lysophospholipids and acyl donors. A variety of membrane-forming cellular phospholipids have been obtained in high yields. Membrane formation takes place in water from natural alkaline sources such as soda lakes and hydrothermal oceanic vents. When formed vesicles are transferred to more acidic solutions, electrochemical proton gradients are spontaneously established and maintained. This high-yielding non-enzymatic synthesis of natural phospholipids in water opens up new routes for lipid synthesis in artificial cells and sheds light on the origin and evolution of cellular membranes.
Collapse
Affiliation(s)
- Luping Liu
- Department of Chemistry and Biochemistry, University of California, San Diego, CA, USA
| | - Yike Zou
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, USA
| | - Ahanjit Bhattacharya
- Department of Chemistry and Biochemistry, University of California, San Diego, CA, USA
| | - Dongyang Zhang
- Department of Chemistry and Biochemistry, University of California, San Diego, CA, USA
| | - Susan Q Lang
- School of the Earth, Ocean, and Environment, University of South Carolina, Columbia, SC, USA
| | - K N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA, USA
| | - Neal K Devaraj
- Department of Chemistry and Biochemistry, University of California, San Diego, CA, USA.
| |
Collapse
|
2
|
A protocell with fusion and division. Biochem Soc Trans 2019; 47:1909-1919. [PMID: 31819942 DOI: 10.1042/bst20190576] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 11/12/2019] [Accepted: 11/25/2019] [Indexed: 11/17/2022]
Abstract
A protocell is a synthetic form of cellular life that is constructed from phospholipid vesicles and used to understand the emergence of life from a nonliving chemical network. To be considered 'living', a protocell should be capable of self-proliferation, which includes successive growth and division processes. The growth of protocells can be achieved via vesicle fusion approaches. In this review, we provide a brief overview of recent research on the formation of a protocell, fusion and division processes of the protocell, and encapsulation of a defined chemical network such as the genetic material. We also provide some perspectives on the challenges and future developments of synthetic protocell research.
Collapse
|
3
|
Bhattacharya A, Brea RJ, Devaraj NK. De novo vesicle formation and growth: an integrative approach to artificial cells. Chem Sci 2017; 8:7912-7922. [PMID: 29619165 PMCID: PMC5858084 DOI: 10.1039/c7sc02339a] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 10/13/2017] [Indexed: 12/22/2022] Open
Abstract
The assembly of synthetic membranes provides a powerful tool to reconstruct the structure and function of living cells.
The assembly of artificial cells provides a novel strategy to reconstruct life's functions and shed light on how life emerged on Earth and possibly elsewhere. A major challenge to the development of artificial cells is the establishment of simple methodologies to mimic native membrane generation. An ambitious strategy is the bottom-up approach, which aims to systematically control the assembly of highly ordered membrane architectures with defined functionality. This perspective will cover recent advances and the current state-of-the-art of minimal lipid architectures that can faithfully reconstruct the structure and function of living cells. Specifically, we will overview work related to the de novo formation and growth of biomimetic membranes. These studies give us a deeper understanding of the nature of living systems and bring new insights into the origin of cellular life.
Collapse
Affiliation(s)
- Ahanjit Bhattacharya
- Department of Chemistry and Biochemistry , University of California, San Diego , La Jolla , CA 92093 , USA .
| | - Roberto J Brea
- Department of Chemistry and Biochemistry , University of California, San Diego , La Jolla , CA 92093 , USA .
| | - Neal K Devaraj
- Department of Chemistry and Biochemistry , University of California, San Diego , La Jolla , CA 92093 , USA .
| |
Collapse
|
4
|
Abstract
Cells produce lipid membranes de novo through a complex sequence of enzymatic reactions that are difficult to reconstitute in a minimal system. We set out to take a different approach and mimic the synthesis of phospholipids using abiotic but highly selective bioconjugation reactions. Here, I outline several of our group's recent advances in exploring chemoselective reactions for stitching together lipid fragments to form membrane-forming lipids from non-membrane-forming precursors. Rapid chemical reactions can be harnessed to achieve facile de novo synthesis of lipid membranes, and spontaneous membrane formation can be applied for the reconstitution of membrane proteins, encapsulation and concentration of nanomaterials, and the study of lipid membrane remodeling. I conclude by briefly outlining future challenges and opportunities.
Collapse
Affiliation(s)
- Neal K Devaraj
- University of California, San Diego , La Jolla, California 92093, United States
| |
Collapse
|
5
|
Self-reproducing catalyst drives repeated phospholipid synthesis and membrane growth. Proc Natl Acad Sci U S A 2015; 112:8187-92. [PMID: 26100914 DOI: 10.1073/pnas.1506704112] [Citation(s) in RCA: 118] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cell membranes are dynamic structures found in all living organisms. There have been numerous constructs that model phospholipid membranes. However, unlike natural membranes, these biomimetic systems cannot sustain growth owing to an inability to replenish phospholipid-synthesizing catalysts. Here we report on the design and synthesis of artificial membranes embedded with synthetic, self-reproducing catalysts capable of perpetuating phospholipid bilayer formation. Replacing the complex biochemical pathways used in nature with an autocatalyst that also drives lipid synthesis leads to the continual formation of triazole phospholipids and membrane-bound oligotriazole catalysts from simpler starting materials. In addition to continual phospholipid synthesis and vesicle growth, the synthetic membranes are capable of remodeling their physical composition in response to changes in the environment by preferentially incorporating specific precursors. These results demonstrate that complex membranes capable of indefinite self-synthesis can emerge when supplied with simpler chemical building blocks.
Collapse
|
6
|
Brea RJ, Cole CM, Devaraj NK. In situ vesicle formation by native chemical ligation. Angew Chem Int Ed Engl 2014; 53:14102-5. [PMID: 25346090 PMCID: PMC4418804 DOI: 10.1002/anie.201408538] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2014] [Indexed: 01/07/2023]
Abstract
Phospholipid vesicles are of intense fundamental and practical interest, yet methods for their de novo generation from reactive precursors are limited. A non-enzymatic and chemoselective method to spontaneously generate phospholipid membranes from water-soluble starting materials would be a powerful tool for generating vesicles and studying lipid membranes. Here we describe the use of native chemical ligation (NCL) to rapidly prepare phospholipids spontaneously from thioesters. While NCL is one of the most popular tools for synthesizing proteins and nucleic acids, to our knowledge this is the first example of using NCL to generate phospholipids de novo. The lipids are capable of in situ synthesis and self-assembly into vesicles that can grow to several microns in diameter. The selectivity of the NCL reaction makes in situ membrane formation compatible with biological materials such as proteins. This work expands the application of NCL to the formation of phospholipid membranes.
Collapse
Affiliation(s)
- Roberto J. Brea
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Building: Urey Hall 4120, La Jolla, CA 92093, USA, Fax: (+1) 858-534-9503, Homepage: http://devarajgroup.ucsd.edu
| | - Christian M. Cole
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Building: Urey Hall 4120, La Jolla, CA 92093, USA, Fax: (+1) 858-534-9503, Homepage: http://devarajgroup.ucsd.edu
| | - Neal K. Devaraj
- Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive, Building: Urey Hall 4120, La Jolla, CA 92093, USA, Fax: (+1) 858-534-9503, Homepage: http://devarajgroup.ucsd.edu
| |
Collapse
|
7
|
Brea RJ, Cole CM, Devaraj NK. In Situ Vesicle Formation by Native Chemical Ligation. Angew Chem Int Ed Engl 2014. [DOI: 10.1002/ange.201408538] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
|
8
|
Murtas G. Internal lipid synthesis and vesicle growth as a step toward self-reproduction of the minimal cell. SYSTEMS AND SYNTHETIC BIOLOGY 2009; 4:85-93. [PMID: 19957048 PMCID: PMC2923298 DOI: 10.1007/s11693-009-9048-1] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Revised: 11/17/2009] [Accepted: 11/18/2009] [Indexed: 10/24/2022]
Abstract
One of the major properties of the semi-synthetic minimal cell, as a model for early living cells, is the ability to self-reproduce itself, and the reproduction of the boundary layer or vesicle compartment is part of this process. A minimal bio-molecular mechanism based on the activity of one single enzyme, the FAS-B (Fatty Acid Synthase) Type I enzyme from Brevibacterium ammoniagenes, is encapsulated in 1-palmitoyl-2oleoyl-sn-glycero-3-phosphatidylcholine (POPC) liposomes to control lipid synthesis. Consequently molecules of palmitic acid released from the FAS catalysis, within the internal lumen, move toward the membrane compartment and become incorporated into the phospholipid bilayer. As a result the vesicle membranes change in lipid composition and liposome growth can be monitored. Here we report the first experiments showing vesicles growth by catalysis of one enzyme only that produces cell boundary from within. This is the prototype of the simplest autopoietic minimal cell.
Collapse
Affiliation(s)
- Giovanni Murtas
- Centro "Enrico Fermi", Via Panisperna 89A, 00184 Rome, Italy
| |
Collapse
|
9
|
Abstract
The continuity of abiotically formed bilayer membranes with similar structures in contemporary cellular life, and the requirement for microenvironments in which large and small molecules could be compartmentalized, support the idea that amphiphilic boundary structures contributed to the emergence of life. As an extension of this notion, we propose here a 'Lipid World' scenario as an early evolutionary step in the emergence of cellular life on Earth. This concept combines the potential chemical activities of lipids and other amphiphiles, with their capacity to undergo spontaneous self-organization into supramolecular structures such as micelles and bilayers. In particular, the documented chemical rate enhancements within lipid assemblies suggest that energy-dependent synthetic reactions could lead to the growth and increased abundance of certain amphiphilic assemblies. We further propose that selective processes might act on such assemblies, as suggested by our computer simulations of mutual catalysis among amphiphiles. As demonstrated also by other researchers, such mutual catalysis within random molecular assemblies could have led to a primordial homeostatic system displaying rudimentary life-like properties. Taken together, these concepts provide a theoretical framework, and suggest experimental tests for a Lipid World model for the origin of life.
Collapse
Affiliation(s)
- D Segré
- Dept. of Molecular Genetics, Crown Human Genome Center, Weizmann Institute of Science, Rehovot 76100, Israel
| | | | | | | |
Collapse
|
10
|
Wick R, Luisi PL. Enzyme-containing liposomes can endogenously produce membrane-constituting lipids. CHEMISTRY & BIOLOGY 1996; 3:277-85. [PMID: 8807855 DOI: 10.1016/s1074-5521(96)90107-6] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
BACKGROUND 'Giant vesicles' are liposomes that have diameters of several micrometers. It is possible to microinject biochemicals into a single vesicle and follow the progress of a chemical reaction in real time by light microscopy. We have previously used this technique to inject phospholipase A2 into giant vesicles; the vesicles disappeared as their components were hydrolyzed. Here we investigate whether the lipid components of a vesicle can be synthesized inside it. RESULTS Giant vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (POPC) and palmitoyl-CoA were prepared in a solution containing sn-glycerol-3-phosphate. Microinjection of the enzyme sn-glycerol-3-phosphate-acyltransferase into the vesicle catalyzes the in situ production of the lipid membrane precursor 1-palmitoyl-sn-glycerol-3-phosphate, which remains incorporated in the membrane. The altered membrane chemistry causes shrinkage of the vesicle and formation of smaller liposomes on the inner surface at the site of injection. Similar transformations were seen when the enzyme was added to the outside of the vesicle. CONCLUSIONS We have used the first step of the 'salvage pathway' for synthesis of POPC to demonstrate that it is possible to localize the synthesis of a lipid membrane precursor inside a giant vesicle. In the future it may be possible to combine the necessary enzymes and substrates to carry out the reactions for a complete metabolic pathway within a liposome.
Collapse
Affiliation(s)
- R Wick
- ETH-Zentrum, Institut für Polymere, Universitätstrasse 6, CH-8092 Zürich, Switzerland.
| | | |
Collapse
|
11
|
Fyrst H, Pham DV, Lubin BH, Kuypers FA. Formation of vesicles by the action of acyl-CoA:1-acyllsophosphatidylcholine acyltransferase from rat liver microsomes: optimal solubilization conditions and analysis of lipid composition and enzyme activity. Biochemistry 1996; 35:2644-50. [PMID: 8611569 DOI: 10.1021/bi952268m] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The enzyme acyl coenzyme A:1-acyllysophosphatidylcholine acyltransferase (acyl-CoA:lysoPC acyltransferase) can be isolated in newly formed phosphatidylcholine (PC) vesicles by solubilization of rat liver microsomes with the two substrates lysoPC and acyl-CoA. In this study, we sought to optimized the conditions for the formation of PC vesicles and analyzed the lipid composition and enzyme activity of the newly formed vesicles. Analysis of PC vesicles formed by incubation of the microsomal preparation with 1-(C16:0)lysoPC and C18:1CoA, C18:2CoA, or C20:4CoA showed that the optimal protein:lysoPC ratio was 1:5 (by weight) and the optimal lysoPC:acyl-CoA ratio was 1:1 (molar amounts). PC formation increased with incubation time; after 20 h of incubation at 37 degrees C, approximately 75% of the lysoPC was converted to PC in the incubation mixture. The phospholipid molecular species composition of the vesicles reflected almost exclusively the substrates used; the vesicles contained approximately 33% of the total acyl-CoA:lysoPC acyltransferase activity from the microsomes and demonstrated a single protein band with a molecular mass of 21 kDa by gel electrophoresis. The procedure selected for the enzyme specific for lysoPC acylation, as enzyme activity toward lysophosphatidylethanolamine (lysoPE), lysophosphatidylserine (lysoPS), and lysophosphatidylinositol (lysoPI), was very low. In addition, the utilization of different acyl-CoA substrates for acylation of lysoPC was different from that in microsomes. These results show that an enzyme specific for the formation of PC from lysoPC can be isolated in PC vesicles with a designed phospholipid molecular species composition and that the lipid environment plays an important role in the regulation of the enzyme's affinity for its substrates.
Collapse
Affiliation(s)
- H Fyrst
- Children's Hospital Oakland Research Institute, Oakland, California 94609, USA
| | | | | | | |
Collapse
|
12
|
Lascu I, Edwards B, Cucuianu MP, Deamer DW. Platelet aggregation is inhibited by long chain acyl-CoA. Biochem Biophys Res Commun 1988; 156:1020-5. [PMID: 3142460 DOI: 10.1016/s0006-291x(88)80946-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Oleoyl coenzyme A and other acyl-CoA derivatives inhibited ADP or thrombin-induced aggregation of platelets. Arachidonic acid-induced aggregation was also inhibited, but not the slower aggregation caused by 1-oleoyl-2-acetylglycerol or tetradecanoyl-phorbol-13-acetate. Coenzyme A and free fatty acids had little or no effect, and transfer of labeled oleate from oleoyl Co-A to other lipid classes was not detected. Because acyl Co-A compounds have recently been shown to modulate protein kinase C activity, acyl Co-A may provide a useful tool for investigating activation sequences in platelets and other membranes.
Collapse
Affiliation(s)
- I Lascu
- Department of Biochemistry, Medical and Pharmaceutical Institute, Cluj-Napoca, Romania
| | | | | | | |
Collapse
|
13
|
Farahbakhsh ZT, Deamer DW, Lee NM, Loh HH. Enzymatic reconstitution of brain membrane and membrane opiate receptors. J Neurochem 1986; 46:953-62. [PMID: 3005499 DOI: 10.1111/j.1471-4159.1986.tb13062.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A new method using lysophosphatide and acyl-CoA as detergents has been used to solubilize the rat brain opiate receptor. After solubilization, lysophosphatide and acyl-CoA can be almost completely removed by an enzymatic reaction that uses an acyltransferase from rat liver microsomes and reconstitutes the solubilized receptor in membranous vesicles. Morphological studies performed with negative staining and freeze-fracture electron microscopy revealed that the general appearance and intramembrane particle distribution of fracture faces in the reconstituted membrane are similar to those of the native membrane; this indicates that hydrophobic protein components of the original membrane were incorporated during reconstitution. Reconstituted membrane, however, contained higher levels of phosphatidylcholine and lower levels of cholesterol. The activities of the membrane-bound enzymes Na+, K+-ATPase and Ca2+, Mg2+-ATPase in the reconstituted system were 24 and 3%, respectively, those of the native membrane. Although binding of opiate ligands to the reconstituted membrane was stereospecific and saturable, higher concentrations of some of the unlabeled ligands were required to inhibit binding of the radiolabeled ligands. These changes in receptor characteristics are likely due to changes in lipid composition, physical state, and/or distribution of the lipids in the reconstituted membrane bilayer. This conclusion is supported by an increase in the affinity of opiate ligands for reconstituted membrane after adjustment of the latter's lipid composition to match more closely that of the original membrane. This was accomplished by treatment with phospholipid exchange protein to remove the excess phosphatidylcholine and by incorporation of cholesterol into the reconstituted membrane.
Collapse
|
14
|
Kawamoto RM, Baskin RJ. Isolation and characterization of sarcoplasmic reticulum from normal and dystrophic chicken. Muscle Nerve 1986; 9:248-56. [PMID: 3010101 DOI: 10.1002/mus.880090309] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Purified sarcoplasmic reticulum vesicles from normal and dystrophic chicken skeletal muscle have been isolated by a procedure employing pressure disruption of a microsomal suspension. The dystrophic sarcoplasmic reticulum (SR) exhibited reduced Ca++ transport and phosphoenzyme formation, but the Ca++-ATPase activity was normal. Normal and dystrophic SR showed similar lipid profiles, except for a significant increase in free fatty acids in the dystrophic SR. Investigations involving the interaction of oleic acid with normal SR showed fatty acids can induce conditions similar to those found in dystrophic SR.
Collapse
|
15
|
Deamer DW, Gavino V. Lysophosphatidylcholine acyltransferase: purification and applications in membrane studies. Ann N Y Acad Sci 1983; 414:90-6. [PMID: 6584078 DOI: 10.1111/j.1749-6632.1983.tb31677.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
|
16
|
Piacentini M, Spinedi A, Beninati S, Autuori F. Mechanism of release of integral proteins from rat liver microsomal membranes. BIOCHIMICA ET BIOPHYSICA ACTA 1983; 731:151-60. [PMID: 6303417 DOI: 10.1016/0005-2736(83)90004-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The release of three integral enzymatic activities (NADH- and NADPH-cytochrome c reductase and 5'-nucleotidase) and total protein from washed rat liver microsomal membranes, upon simple incubation at 37 degrees C in aqueous media, was investigated. Release does not depend on contaminating proteases and is enhanced by alkaline pH. Total protein and enzyme release is consistent with a loss of phospholipids which are not recovered in the soluble phase. Following incubation at pH 9.0 large amounts of free fatty acids were recovered in the soluble phase, accounting for a ratio of 1/1 (w/w) with released protein. This evidence, together with the data available about densities (1.07-1.08 g/ml) and molecular weights (1 700 000-700 000) of the released enzymes, suggests that they are solubilized from microsomal membranes in the form of mixed micelles mostly formed by free fatty acids and integral proteins, probably owing to the activity of endogenous phospholipases on membrane lipids. Release of total protein and enzymatic activities is decreased by Ca2+, whose possible role in the phenomenon is discussed.
Collapse
|
17
|
Gavino VC, Deamer DW. Purification of acyl CoA:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase. J Bioenerg Biomembr 1982; 14:513-26. [PMID: 7161282 DOI: 10.1007/bf00743075] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Acyl coenzyme A:1-acyl-sn-glycero-3-phosphorylcholine acyltransferase (EC 2.3.1.23) is capable of forming lipid bilayer vesicles from its soluble substrates lysophosphatidylcholine (LPC) and oleoyl CoA. This suggested a purification method in which rat liver microsomes are first washed with deoxycholate to increase specific activity of the endogenous acyltransferase approximately fivefold, then solubilized by the detergent effect of excess LPC and oleoyl CoA in 1:1 stoichiometric ratios. As the LPC is converted to phosphatidylcholine by acyl group transfer, the detergent effect is lost and lipid vesicles containing the enzyme activity are produced. Other microsomal proteins are excluded from the vesicles. The vesicles may be separated by density gradient flotation and are found to contain acyltransferase with a specific activity of 9-10 mu mol/mg/min. This reflects a purification of approximately 140-fold, about ten times greater than achieved in previous studies.
Collapse
|