Unit Converter
Pyrrolysine (Pyl)
(The 22nd Genetically Encoded Amino Acid - Present in Archaea & Some Bacteria; Not a Human Metabolite)
Synonyms
- Pyrrolysine
- Pyl
- L-pyrrolysine
- Genetic code 22nd amino acid
- O-methyl-pyrroline-carboxylate–lysine
Units of Measurement
(For biochemical/laboratory reference only; NOT routinely measured in humans)
- µmol/L
- mg/L
- mg/dL
- mg/100mL
- mg%
- µg/mL
Molecular Weight
255.3 g/mol
Key Unit Conversions
(Calculated from molecular weight; used if studying Pyl experimentally)
Mass ↔ Molar
1 mg/L=3.92 µmol/L1\ \text{mg/L} = 3.92\ \text{µmol/L}1 mg/L=3.92 µmol/L 1 µmol/L=0.255 mg/L1\ \text{µmol/L} = 0.255\ \text{mg/L}1 µmol/L=0.255 mg/L
mg/dL ↔ mg/L
1 mg/dL=10 mg/L1\ \text{mg/dL} = 10\ \text{mg/L}1 mg/dL=10 mg/L
µg/mL
1 µg/mL=1 mg/L1\ \text{µg/mL} = 1\ \text{mg/L}1 µg/mL=1 mg/L
mg%
\text{mg%} = \text{mg/dL}
Description
Pyrrolysine (Pyl) is a rare, naturally occurring amino acid incorporated into proteins by certain:
- Methanogenic archaea
- Bacteria (e.g., Desulfitobacterium)
It is genetically encoded by the UAG “amber” stop codon, which is reassigned in these organisms via:
- A specialized tRNA^Pyl
- A dedicated pyrrolysyl-tRNA synthetase
Pyl participates in:
- Methane metabolism
- Methyltransferase enzyme activity
- Anaerobic respiratory pathways
In humans, pyrrolysine is not used in proteins, not synthesized, and not measured clinically.
Physiological Role (Non-human)
In archaea & bacteria:
- Essential for methanogenesis
- Improves catalytic activity of methylamine methyltransferases
- Expands the genetic code to include a 22nd proteinogenic amino acid
No physiological role in humans.
Clinical Significance
⚠️ Pyrrolysine has no known direct clinical relevance in human medicine.
It is not a human metabolite and not involved in human metabolic, endocrine, or nutritional pathways.
However, it has research and biotechnology relevance:
1. Synthetic Biology
Pyl system (tRNA^Pyl & PylRS enzyme) is widely used for:
- Genetic code expansion
- Incorporation of unnatural amino acids
- Designer proteins and therapeutics
2. Microbiology Research
Helps identify:
- Methanogenic species
- Bacterial pathways in environmental biochemistry
3. Evolutionary Biology
Evidence of natural genetic code expansion beyond the canonical 20 amino acids.
Reference Intervals
No reference ranges exist because pyrrolysine is not present in human plasma or tissues.
Clinical labs do not measure Pyl in:
- Plasma
- Serum
- Urine
- CSF
- Newborn screening
- Amino-acid panels
Diagnostic Uses
None in human diagnostics.
But Pyl is valuable in:
1. Microbial Identification (Research)
Marker of:
- Methanogenic archaea
- Anaerobic respiration pathways
2. Genetic Code Engineering
Allows insertion of:
- Fluorescent amino acids
- Photo-sensitive amino acids
- Drug-conjugated residues
3. Protein Engineering
Used to create:
- Novel antibodies
- Enzyme modifications
- Targeted therapeutics
Analytical Notes
- Detected by HPLC or LC–MS/MS in microbial studies
- Not part of clinical amino-acid panels
- Chemically stable cyclic-lysine derivative
Clinical Pearls
- Pyrrolysine is NOT a human amino acid, unlike proline, lysine, valine, etc.
- Plays no role in human nutrition or metabolism.
- Included here for completeness because some amino-acid glossaries list it.
- Important in synthetic biology, not in clinical biochemistry.
Interesting Fact
Pyrrolysine is encoded by a reassigned stop codon (UAG) - making it one of only two naturally occurring amino acids beyond the “canonical 20,” the other being selenocysteine (Sec/U).
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Amino Acid Biochemistry (Non-human notes)
- ACMG & Analytical Biochemistry - Amino Acid Pathways
- Mayo Clinic / ARUP - Amino Acid Panels (exclusion of Pyl)
- Science, Nature, PNAS - Studies on Pyrrolysine in Archaea/Bacteria
- Genetics & Synthetic Biology Sources - PylRS/Pyl-tRNA applications