Effect of Independent Variations in Fatty Acid Structure and Chain Length on Lipid Polar Headgroup Composition in<i>Acholeplasma laidlawii</i>B Membranes: Regulation of Lamellar/Nonlamellar Phase Propensity
Bibliographic record
Abstract
We have studied the biosynthetic regulation of the membrane lipid polar headgroup distribution in Acholeplasma laidlawii B cells made fatty acid auxotrophic by growth in the presence of the biotin-binding agent avidin to test whether this organism has the ability to coherently regulate the lamellar/nonlamellar phase propensity of its membrane lipids. The addition of various single normal growth-supporting exogenous fatty acids to such cell cultures produces fatty acid-homogeneous cells in which the hydrocarbon chain length and structure of the fatty acyl chains of the membrane lipids can be independently varied. Moreover, in analyzing our results, we consider the fact that the individual membrane lipid classes of this organism can form either normal micellar, lamellar, or reversed cubic or hexagonal phases in isolation (Lewis, R. N. A. H., and McElhaney, R. N. (1995) Biochemistry 34, 13818-13824). When A. laidlawii cells are highly enriched in one of a homologous series of methyl isobranched, methyl anteisobranched, or omega-cyclohexyl fatty acids, neither the ratio of normal micellar/lamellar nor of inverted cubic or hexagonal/lamellar phase-forming lipids are coherently regulated, and in fact in the former case, the changes in lipid polar headgroup composition observed are generally in a direction opposite to that required to maintain the overall lamellar/nonlamellar phase preference of the total membrane lipids constant when hydrocarbon chain length is varied. Similarly, when lipid hydrocarbon structure is varied at a constant effective chain length, a similar lack of coherent regulation of membrane lipid polar headgroup distribution is also observed, although in this case a weak overall trend in the expected direction occurs. We also confirm our previous finding (Foht, P. J., Tran, Q. M., Lewis, R. N. A. H., and McElhaney, R. N. (1995) Biochemistry 34, 13811-13817) that the ratio of inverted phase-forming monoglucosyl diacylglycerol to the lamellar phase-forming glycolipid diglucosyl diacylglycerol, previously used to estimate membrane lipid phase preference in A. laidlawii A and B, is not by itself a reliable indicator of the overall lamellar/nonlamellar phase propensity of the total membrane lipids of these organisms. Our results indicate that A. laidlawii B lacks a coherent mechanism to biosynthetically regulate the polar headgroup distribution of its membrane lipids to maintain the micellar/lamellar/inverted phase propensity constant in the face of induced variations in either the chain length or the structure of its lipid hydrocarbon chains. Finally, we suggest that the lack of a coherent regulatory mechanism to regulate the overall phase-forming propensity of the total membrane lipids of this organism under these circumstances may result in part from its inability to optimize all of the biologically relevant physical properties of its membrane lipid bilayer simultaneously.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".