What are the molecular weights of natamycin and amphotericin B?

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Molecular Weight Comparison: Natamycin vs Amphotericin B

Natamycin has a molecular weight of 665 Da, while amphotericin B has a molecular weight of 924-926 Da, making amphotericin B approximately 40% larger than natamycin.

Molecular Weight Data

Amphotericin B

  • Molecular weight: 924-926 Da 1
  • Mass spectrometry studies using both plasma desorption and electron-impact methods confirmed amphotericin B has a molecular weight of 926 1
  • The structure contains 47 carbons with a polyene macrolide ring system 1

Natamycin (Pimaricin)

  • Molecular weight: 665 Da 2, 3
  • Natamycin is a smaller polyene macrolide antibiotic compared to amphotericin B 2
  • Despite both being polyene antifungals, natamycin's smaller molecular size contributes to different pharmacokinetic properties 2

Clinical Implications of Size Difference

Membrane Penetration

  • The smaller molecular weight of natamycin allows substantially higher corneal uptake compared to amphotericin B in ophthalmic applications 2
  • In corneas with intact epithelium, natamycin achieved 7.0 μg/g tissue concentration at 2 minutes, while amphotericin B achieved only 0.23 μg/g 2
  • Both drugs can penetrate debrided corneal stroma, but natamycin's smaller size provides superior penetration through intact epithelium 2

Mechanism of Action Differences

  • Despite both recognizing membrane sterols, the molecular size difference results in distinct interaction patterns 4
  • Amphotericin B causes cooperative membrane perturbation with marked increases in membrane linewidth, reflecting extensive bilayer disruption 4
  • Natamycin engages sterols selectively and non-cooperatively, with minimal impact on overall membrane structure 4
  • The smaller natamycin molecule docks on the opposite sterol face compared to amphotericin B, using a head-to-tail model similar to amphotericin B but with different sterol engagement 4

Analytical Considerations

  • The molecular weight difference allows for effective separation by HPLC, with natamycin (retention time 6 minutes) eluting before amphotericin B (retention time 15 minutes) 3
  • Natamycin can serve as an internal standard for amphotericin B analysis due to the distinct molecular weights and UV absorption properties 3

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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