Hypochlorous Acid Metabolic Process Terms — Obsoletion

SCOPING OBSOLETION

Species: mouse

Hypochlorous Acid Metabolic Process Terms — Obsoletion

Bottom line: GO has obsoleted all three hypochlorous acid (HOCl)
process terms: the grouping term GO:0002148 went first, and OLS now lists
the biosynthetic (GO:0002149) and catabolic (GO:0002150) terms as obsolete
too. Their obsolete definitions give the final reason, "this BP term
represents a MF term"; the originating ticket (go-ontology#22891) had
instead flagged the wrong is_a parent (see Overview). HOCl is made in one
enzymatic step, myeloperoxidase turning H2O2 and chloride into HOCl, so a
process term adds nothing to the enzyme activity. We inventoried the
annotations: one mouse Mpo IMP row (MGI, PMID:10085024), one rat Mpo ISO
row copied from it, and nothing on the catabolic term. No review in this
repo uses these terms and Mpo is not reviewed. Scoped, not yet started:
the status notes below predate the obsoletion, and the molecular function
an earlier draft proposed as the anchor was wrong: OLS labels GO:0140825
lactoperoxidase activity, not an HOCl-forming chloride peroxidase
activity (corrected in the body below).

Overview

A GO obsoletion proposal targets three biological-process terms in the
hypochlorous acid (HOCl) branch:

The two rationales come from different stages. The originating ticket,
go-ontology#22891, argued that the original parentage
(is_a organic acid metabolic process, GO:0006082) is incorrect because
hypochlorous acid contains no carbon and so is not an organic acid. The
grouping-term obsoletion at the parent level (go-ontology#30524) already
removed GO:0002148, which had no remaining annotations. The two child terms
carried annotations and needed a curatorial decision first. When they were
obsoleted, the reason recorded in their definitions was different: "The
reason for obsoletion is that this BP term represents a MF term" (OLS,
GO:0002149), i.e. HOCl formation is a single enzymatic step best captured
as an MF.

This project tracks the impact on AI Gene Review. No genes in scope are
currently reviewed here.

Upstream tickets

Annotation inventory (verified via QuickGO 2026-05-20)

Aspect Term Gene UniProt Taxon Evidence Reference Assigned by Qualifier
BP GO:0002149 hypochlorous acid biosynthetic process Mpo P11247 NCBITaxon:10090 (mouse) IMP PMID:10085024 MGI acts_upstream_of_or_within
BP GO:0002149 hypochlorous acid biosynthetic process Mpo A0A0G2K1A2 NCBITaxon:10116 (rat) ISO (ECO:0000266) GO_REF:0000121 RGD acts_upstream_of_or_within (with-from MGI:97137 = mouse Mpo)
BP GO:0002150 hypochlorous acid catabolic process — — — — — — (no direct protein annotations returned by QuickGO)

The rat annotation is ISO-propagated from the mouse one; if the mouse
annotation is migrated, the rat record will follow automatically through
the next ISO pipeline. The catabolic-process term (GO:0002150) appears to
have no direct protein annotations, so its obsoletion is purely
terminological.

Why this fits AI Gene Review

Single concrete gene: mouse myeloperoxidase (Mpo, P11247). Myeloperoxidase
is the textbook HOCl-generating enzyme of neutrophils (RHEA:43232,
EC 1.11.2.2; H2O2 + Cl- + H+ → HOCl + H2O). The enzyme catalyzes one well-defined reaction whose product is HOCl.
An earlier draft of this page named GO:0140825 as the precise MF term
for it, but OLS labels GO:0140825 lactoperoxidase activity ("2 a phenolic
donor + H2O2 = 2 a phenolic radical donor + 2 H2O"), which is not the
HOCl-forming reaction. The nearest GO term found by name,
GO:0016691 chloride peroxidase activity, is defined as organic
chlorination ("2 R-H + 2 chloride + H2O2 = 2 R-Cl + 2 H2O"), so whether GO
has an MF term matching RHEA:43232 still needs checking (checked in OLS,
2026-09-26).
The pending obsoletion is therefore a clean Type B refresh:

Note: GO:0042554 superoxide anion generation is not a defensible
target for Mpo — that term is the NADPH-oxidase (NOX2/CYBB) step
upstream of Mpo in the respiratory burst (NADPH oxidase → O2•- → SOD
→ H2O2 → Mpo → HOCl); Mpo consumes H2O2 rather than generating
superoxide.

The upstream go-annotation#6404 body does not list a chosen replacement,
so this remains passive tracking until the upstream decision lands.

Impact on this repo

Candidate gene for review (deferred)

Tier Gene Organism UniProt Existing in repo? Notes
1 Mpo (myeloperoxidase) Mus musculus P11247 No Only gene with a direct IMP annotation to GO:0002149. Carries 20+ other GOA rows; a full /review would cover the broader heme-peroxidase / neutrophil-degranulation context.
(follow-on) Mpo Rattus norvegicus A0A0G2K1A2 No ISO descendant; will follow the mouse migration automatically.
(follow-on) MPO Homo sapiens P05164 No Not in the upstream affected list (no direct GO:0002149 annotation) but is the human ortholog and the textbook reference for the activity; reviewing only if the upstream replacement term is interesting cross-organism.

Proposed approach

  1. Wait for upstream replacement-term decision. The current upstream
    ticket #6404 has zero comments and the ontology ticket #22891 only
    raises the is-a parentage problem; no obsoletion PR has been opened.
    There is no point migrating the annotation before the target is
    chosen, since the current MGI IMP row is otherwise well-evidenced
    (PMID:10085024).
  2. When upstream lands, run just fetch-gene mouse Mpo and do a full
    /review — Mpo is a high-yield review target regardless of the
    obsoletion (peroxidase MF, neutrophil/granule CC, immune-defense BP,
    well-cited literature).
  3. Identify the MF term for HOCl formation (RHEA:43232, EC 1.11.2.2)
    for Mpo's core_functions. Do not use GO:0140825, which is
    lactoperoxidase activity; check whether GO:0016691 chloride
    peroxidase activity     (defined as organic chlorination) fits, or whether
    a new term is needed.
  4. Defer the rat ISO row — it will follow the mouse migration
    automatically through the standard ISO pipeline.

Priority

Low. Only one direct experimental annotation is affected, the
obsoletion has no chosen target yet upstream, and the affected gene
(Mpo) is not currently reviewed here. The opportunity is that Mpo is
an otherwise unreviewed, well-characterized mammalian heme peroxidase
that would extend the repo's mouse coverage, not that any existing
review is blocked.

Status

Slides