| Aspect | Evidence summary | Key quantitative data |
|---|---|---|
| Target identity | UniProt Q88LG1 corresponds to **tyrB / PP_1972** in *Pseudomonas putida* KT2440; genome annotation in KT2440 literature lists **PP1972** as **tyrB-1**, one of two tyrosine/aromatic aminotransferase-like genes in this strain (pqac-00000005, pqac-00000008) | Locus tags/names reported as **PP1972 / tyrB-1**; paralog also noted as **PP3590 / tyrB-2** (pqac-00000005) |
| Predicted molecular function/class | TyrB/PP_1972 is an **aminotransferase** in the **PLP-dependent aromatic amino acid aminotransferase** class; related *P. putida* aromatic aminotransferases preferentially transaminate aromatic amino acids with 2-oxoglutarate, with best substrates including **L-phenylalanine** and **phenylpyruvate** (pqac-00000000, pqac-00000001, pqac-00000007) | Assays for related *P. putida* ArAT enzymes used **10 µM PLP** and **3 mM 2-oxoglutarate**; activity measured as release of **1 µmol IPyA min⁻¹** in L-tryptophan:2-oxoglutarate assays (pqac-00000000) |
| Pathway role in aromatic amino acid metabolism | In KT2440, phenylalanine can be degraded by the **phenylalanine hydroxylase pathway** (PhhAB → tyrosine → p-hydroxyphenylpyruvate → homogentisate), and KT2440 carries two TyrB-like aminotransferase genes. Mutant phenotypes support TyrB-family participation in **phenylalanine/tyrosine catabolism**, especially downstream aromatic transamination steps (pqac-00000004, pqac-00000005) | Wild type doubling times on sole N source: **phenylalanine ~8 h**, **tyrosine ~1.8 h**; **tyrB-1** mutant: phenylalanine ~WT, tyrosine **~3.2 h**; **tyrB-2** mutant: phenylalanine **~12 h**, tyrosine **~3.0 h** (pqac-00000004, pqac-00000009) |
| Evidence for redundancy | Recent RB-TnSeq and prior knockout work indicate **functional redundancy** among aromatic aminotransferases in *P. putida* KT2440: PP_1972 has only weak single-gene phenotypes in some aromatic N-source conditions, and even combined loss with PP_3590 did not cause phenylalanine auxotrophy (pqac-00000002, pqac-00000003, pqac-00000006) | BarSeq fitness effects for **PP_1972** were small: phenylalanine **-0.35** and pipecolate **-0.15** in one report; another excerpt summarizes similarly weak effects and cites no phenylalanine auxotrophy in the **PP_3590 PP_1972** double knockout (pqac-00000002, pqac-00000003) |
| Strength/limits of direct evidence for Q88LG1 | Evidence for **PP_1972/Q88LG1 specifically** is mainly **genetic/fitness-based** in KT2440; direct biochemical characterization in *P. putida* has more clearly identified other aromatic aminotransferase isozymes (**tyrB-2/phhC**) than PP_1972 itself, so annotation of Q88LG1 is supported by homology plus mutant evidence rather than purified-enzyme kinetics (pqac-00000001, pqac-00000003, pqac-00000007) | No direct purified-enzyme kinetic constants for **PP_1972/Q88LG1** were extracted from the cited KT2440 sources; strongest KT2440-specific quantitative data are mutant doubling times and RB-TnSeq fitness values (pqac-00000003, pqac-00000009) |


*Table: This table summarizes the strongest available evidence for functional annotation of *Pseudomonas putida* KT2440 tyrB (PP_1972; UniProt Q88LG1), including its identity, predicted aminotransferase role, pathway context, redundancy, and the key quantitative phenotypes available from mutant and fitness studies.*