GO_REF:0000002

GO reference used by source annotation pipeline

Source annotation pipeline provenance for Pfkfb4 annotations including ATP binding; catalytic activity; fructose 2,6-bisphosphate metabolic process; fructose metabolic process.

"GO_REF entry used only to trace source annotation method; biological support was assessed from UniProt and cached literature where available."

GO_REF:0000033

GO reference used by source annotation pipeline

Source annotation pipeline provenance for Pfkfb4 annotations including 6-phosphofructo-2-kinase activity; cytosol.

"GO_REF entry used only to trace source annotation method; biological support was assessed from UniProt and cached literature where available."

GO_REF:0000114

GO reference used by source annotation pipeline

Source annotation pipeline provenance for Pfkfb4 annotations including fructose 2,6-bisphosphate metabolic process.

"GO_REF entry used only to trace source annotation method; biological support was assessed from UniProt and cached literature where available."

GO_REF:0000120

GO reference used by source annotation pipeline

Source annotation pipeline provenance for Pfkfb4 annotations including 6-phosphofructo-2-kinase activity; fructose-2,6-bisphosphate 2-phosphatase activity.

"GO_REF entry used only to trace source annotation method; biological support was assessed from UniProt and cached literature where available."

GO_REF:0000121

GO reference used by source annotation pipeline

Source annotation pipeline provenance for Pfkfb4 annotations including 6-phosphofructo-2-kinase activity.

"GO_REF entry used only to trace source annotation method; biological support was assessed from UniProt and cached literature where available."

PMID:15581487

Regulation of the regulatory enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase

For Pfkfb4, this publication was reviewed as context for gluconeogenesis; glycolytic process. Cached PubMed record has no abstract/full text available, so the title is retained with full_text_unavailable.

"Regulation of the regulatory enzyme, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase."

PMID:1651918

Molecular cloning of the DNA and expression and characterization of rat testes fructose-6-phosphate,2-kinase:fructose-2,6-bisphosphatase

For Pfkfb4, this publication supports direct annotations to 6-phosphofructo-2-kinase activity; fructose-2,6-bisphosphate 2-phosphatase activity.

"We have isolated and sequenced two overlapping cDNA fragments which could encode the complete amino acid sequence of rat testis fructose-6-phosphate,2-kinase:fructose-2,6-bisphosphatase."

PMID:8805587

The crystal structure of the bifunctional enzyme 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase reveals distinct domain homologies

For Pfkfb4, this publication was reviewed as context for 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase complex.

"RESULTS: We have determined the 2.0 A crystal structure of the rat testis isozyme of this bifunctional enzyme."

file:rat/Pfkfb4/Pfkfb4-deep-research-falcon.md

Falcon (Edison Scientific) deep research report: Pfkfb4 (rat, UniProt P25114) functional annotation

Falcon confirms the gene identity (UniProt P25114, rat Pfkfb4) as the testis-type member of the bifunctional PFKFB1-4 family, with two independent catalytic domains.

"PFKFB enzymes are **bifunctional homodimers** with **two independent catalytic domains**: an **N-terminal kinase (PFK-2)** domain that synthesizes F-2,6-BP and a **C-terminal phosphatase (FBPase-2)** domain that degrades F-2,6-BP."
Falcon corroborates the two opposing catalytic activities and their EC numbers, consistent with the existing kinase and phosphatase annotations.

"Fructose-2,6-bisphosphate is produced from fructose-6-phosphate by **6-phosphofructo-2-kinase (PFK-2; EC 2.7.1.105)** and hydrolyzed by **fructose-2,6-bisphosphatase (FBPase-2; EC 3.1.3.46)**; in mammals these opposing activities occur within the same bifunctional PFKFB enzymes."
Falcon describes the metabolic role of fructose-2,6-bisphosphate as a potent allosteric regulator that activates PFK1 and inhibits fructose-1,6-bisphosphatase, supporting the glycolysis and gluconeogenesis process annotations as downstream regulatory context.

"At **submicromolar concentrations**, it stimulates glycolysis and inhibits gluconeogenesis by:"
Falcon supports the cytosolic localization annotation as the primary family-level evidence, noting nuclear staining is a human-cancer context not to be generalized to rat.

"**Cellular component:** primary evidence supports a **cytosolic** enzyme family location; nuclear staining has been observed in a human COAD context but should not be treated as canonical for rat without direct validation."
Falcon confirms the testis-enriched expression matching the UniProt testis-type isozyme identity.

"PFKFB4 is repeatedly described as being **mainly expressed in the testes** and as the **testis isoform** within the four PFKFB genes"
Falcon notes PFKFB4 has a kinase-biased activity ratio (recombinant human kinase ~4.3-fold greater than phosphatase), consistent with retaining both catalytic activities as core functions.

"Recombinant PFKFB4 kinase activity 4.3-fold greater than phosphatase activity"