Is there a peptide that starts with the letter R?

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Yes, Relaxin is a Peptide That Starts with "R"

Relaxin is a well-characterized peptide hormone that begins with the letter R and belongs to the insulin superfamily of peptides. 1

Relaxin Family Peptides

The relaxin family comprises multiple peptides, several of which start with "R":

  • Relaxin (H2 relaxin/RLN2): The primary circulating form in humans, produced by the corpus luteum during pregnancy 1
  • H1 relaxin (RLN1): A human-specific form encoded by a separate gene 1
  • Relaxin-3 (H3 relaxin/RLN3): Present in humans, rats, and mice, primarily expressed in the brain 1

Structural Characteristics

Relaxin is a 6-kDa polypeptide hormone with the following features:

  • Two-chain structure: Consists of separate A and B chains connected by disulfide bonds, similar to insulin 1, 2
  • Conserved receptor-binding motif: Contains the sequence Arg-X-X-X-Arg-X-X-Ile/Val on the B chain, which is highly conserved across species despite significant sequence variation elsewhere in the molecule 1, 2
  • Molecular weight: Approximately 6000 daltons 2, 3

Receptor Interactions

Relaxin peptides bind to specific G-protein coupled receptors:

  • RXFP1 (formerly LGR7): Primary receptor for H2 relaxin, with binding affinity order of H2 relaxin > H1 relaxin > H3 relaxin > INSL3 1
  • RXFP3 (formerly GPCR135): Receptor for H3 relaxin (relaxin-3) 1

Physiological Roles

Relaxin functions as a reproductive hormone with multiple actions:

  • Connective tissue remodeling: Facilitates structural changes in target tissues during pregnancy and parturition 4
  • Uterine effects: Stimulates uterine growth, vascularization, and extracellular matrix remodeling 3
  • Cardiovascular adaptations: Involved in maternal vascular changes during pregnancy 3

References

1
Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

2
Research

Relaxin and its role in pregnancy.

Endocrinology and metabolism clinics of North America, 1995

4
Research

The role of relaxin in human reproduction.

Clinical reproduction and fertility, 1983

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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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