Cytoplasmic NADP-dependent malic enzyme (NADP-ME; EC 1.1.1.40) that oxidatively decarboxylates (S)-malate to pyruvate with release of CO2 and generation of NADPH, requiring a divalent metal cation (Mg2+ or Mn2+); it also supports oxaloacetate decarboxylation. As a plant NADP-ME it links malate metabolism to pyruvate production and NADPH supply for biosynthesis and redox homeostasis. Deep-research literature (falcon) confirms the conserved enzyme identity and reaction but notes that the gene symbol "MAOX" could not be verified against a Populus trichocarpa name for P34105 in the accessible literature, so gene-symbol-specific claims are treated cautiously and the annotation is anchored to the UniProt accession and conserved NADP-ME family biology.
The preferred accession for this review is P34105. These relationships are manually assessed.
REFERENCE PROTEOME EQUIVALENT · Reviewed 2026-10-19
Reference proteome: UP000006729
Retain P34105 as the primary Swiss-Prot accession. B9ILT5 at POPTR_018G086700 is the manually assessed reference-proteome counterpart: 584/591 identical residues with full ungapped coverage. Its seven differences are Y53F, H60Q, T84A, I204M, R251K, I413T, and Q457E. It is clearly separated from other malic-enzyme loci in the full-proteome search and global alignments. The original material is hybrid clone 064; sequence equivalence is assessed at the protein/locus level, not as literal identity or proof of parental origin.
MMseqs2 searched all 77,340 sequences in UP000006729 (release 2026_03); global BLOSUM62 alignments were computed for every returned hit. B9ILT5 ranks first by global alignment score, with 98.8156% identity including gap columns, 100.0% query coverage and 100.0% target coverage. The saved candidate table and alignments retain competing matches and residue-level differences. The search is heuristic, and sequence similarity alone is not definitive genomic mapping. Identity over paired residues is 98.8156% (584/591); gap columns are excluded from this denominator.
file:POPTR/MAOX/MAOX-record-evidence.yaml
query_length: 591 target_length: 591 alignment_columns: 591 identities: 584 mismatches: 7 gap_columns: 0 identity_percent: 98.8156 query_coverage_percent: 100.0 target_coverage_percent: 100.0
Current UniProtKB and proteome records place B9ILT5, but not P34105, in reference proteome UP000006729. Both UniProt records use NCBITaxon:3694; source-organism qualifications are recorded separately.
file:POPTR/MAOX/MAOX-record-evidence.yaml
reference_proteome: UP000006729 proteome_is_reference: true proteome_taxon_matches: true primary_in_reference_proteome: false alternative_in_reference_proteome: true
UniSave versions 101 (2015), 118 (2020), and 132 (2024) lack Proteomes cross-references. These dated samples support longstanding absence at those dates; they do not establish uninterrupted absence, a removal event, or UniProt's motivation.
file:POPTR/MAOX/MAOX-record-evidence.yaml
sampled_history_versions: - 101 - 118 - 132 sampled_versions_with_proteome_links: []
The primary publication identifies the source material as Populus deltoides x Populus trichocarpa clone 064. ENA X56233 has inconsistent taxonomic text (P.deltoides in its description but P. trichocarpa in its organism field); the publication resolves the experimental source as a hybrid.
file:POPTR/MAOX/MAOX-record-evidence.yaml
Organism: Populus deltoides x Populus trichocarpa, clone 064
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0004470 malic enzyme activity | IEA GO_REF:0000002 | MODIFY | Summary: Malic enzyme activity is correct but less specific than the NADP-dependent decarboxylating activity. Reason: UniProt specifies NADP-dependent malate dehydrogenase (decarboxylating) activity with EC 1.1.1.40, and deep-research literature defines this plant NADP-ME as an oxidative decarboxylase catalyzing L-malate + NADP+ to pyruvate, CO2, and NADPH; the more specific GO:0004473 captures the NADP cofactor and decarboxylating direction. Proposed replacements: malate dehydrogenase (decarboxylating) (NADP+) activity Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt Reaction=(S)-malate + NADP(+) = pyruvate + CO2 + NADPH; file:POPTR/MAOX/MAOX-deep-research-falcon.md is typically defined in plant biochemistry as an **oxidative decarboxylase** |
| GO:0004473 malate dehydrogenase (decarboxylating) (NADP+) activity | IEA GO_REF:0000120 | ACCEPT | Summary: NADP-dependent malate dehydrogenase decarboxylating activity is the core molecular function. Reason: The UniProt catalytic reaction is (S)-malate plus NADP(+) to pyruvate, CO2, and NADPH, and deep-research literature independently confirms this conserved plant NADP-ME reaction with a divalent metal cation requirement. Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt Reaction=(S)-malate + NADP(+) = pyruvate + CO2 + NADPH; file:POPTR/MAOX/MAOX-deep-research-falcon.md NADP-ME requires **NADP+** as electron acceptor and a **divalent cation**, typically **Mg2+ or Mn2+**, for activity. |
| GO:0005737 cytoplasm | IEA GO_REF:0000044 | ACCEPT | Summary: Cytoplasm localization is directly supported. Reason: UniProt places MAOX in the cytoplasm. Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm |
| GO:0006108 malate metabolic process | IEA GO_REF:0000117 | ACCEPT | Summary: Malate metabolic process is appropriate for malic enzyme. Reason: The enzyme directly consumes malate in the NADP-dependent decarboxylating reaction, and deep-research literature positions plant NADP-ME as the node linking malate metabolism to pyruvate production, CO2 release, and NADPH generation in central carbon metabolism. Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt Reaction=(S)-malate + NADP(+) = pyruvate + CO2 + NADPH; file:POPTR/MAOX/MAOX-deep-research-falcon.md NADP-ME links **malate metabolism**, **pyruvate production**, **CO2 release**, and **NADPH generation** |
| GO:0008948 oxaloacetate decarboxylase activity | IEA GO_REF:0000116 | ACCEPT | Summary: Oxaloacetate decarboxylase activity is supported as an additional catalytic activity. Reason: UniProt includes the oxaloacetate to pyruvate and CO2 reaction. Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt Reaction=oxaloacetate + H(+) = pyruvate + CO2; |
| GO:0016616 oxidoreductase activity, acting on the CH-OH group of donors, NAD or NADP as acceptor | IEA GO_REF:0000002 | MODIFY | Summary: The broad oxidoreductase term should be replaced by the specific NADP-dependent malic enzyme activity. Reason: UniProt provides the specific malate dehydrogenase (decarboxylating) NADP-dependent reaction, and deep-research literature confirms NADP+ (not NAD+) as the electron acceptor for this enzyme, so the specific GO:0004473 better captures the cofactor and reaction than the broad NAD-or-NADP oxidoreductase grouping term. Proposed replacements: malate dehydrogenase (decarboxylating) (NADP+) activity Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt Reaction=(S)-malate + NADP(+) = pyruvate + CO2 + NADPH; file:POPTR/MAOX/MAOX-deep-research-falcon.md NADP-ME requires **NADP+** as electron acceptor and a **divalent cation**, typically **Mg2+ or Mn2+**, for activity. |
| GO:0051287 NAD binding | IEA GO_REF:0000002 | MODIFY | Summary: NAD binding is structurally supported, but NADP binding is the better primary cofactor term for this NADP-dependent malic enzyme. Reason: UniProt feature annotations include NAD(+) binding positions and NAD(P)-binding domains, but the reviewed protein name, keyword, and primary malic enzyme reaction specify NADP(+); this MODIFY therefore targets the primary catalytic cofactor rather than denying structural NAD binding. Proposed replacements: NADP binding Supporting Evidence: file:POPTR/MAOX/MAOX-uniprot.txt Reaction=(S)-malate + NADP(+) = pyruvate + CO2 + NADPH; file:POPTR/MAOX/MAOX-uniprot.txt FT BINDING 335..351 file:POPTR/MAOX/MAOX-uniprot.txt FT BINDING 192 file:POPTR/MAOX/MAOX-deep-research-falcon.md NADP-ME requires **NADP+** as electron acceptor and a **divalent cation**, typically **Mg2+ or Mn2+**, for activity. |
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Download this section (compressed HTML)Q: What physiological context drives Populus cytosolic NADP-malic enzyme activity, particularly in roots?
Q: Is the gene symbol "MAOX" the accepted Populus trichocarpa name for UniProt P34105, and to which Populus genome locus does P34105 map among the multiple cytosolic and plastidic NADP-ME isoforms?
Experiment: Measure NADP-malic enzyme activity and malate/pyruvate/NADPH pools in MAOX perturbation lines under root stress conditions.
Type: targeted functional assay
Experiment: Confirm cytosolic versus plastidic localization of the P34105 isoform in Populus trichocarpa by fluorescent-protein fusion or subcellular fractionation, to resolve the family-level localization ambiguity.
Type: subcellular localization
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