Question: In which way is apoenzyme a protein?
About the article "Biomolecule", section "Apoenzymes".

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In enzymology, a holo-[acyl-carrier-protein] synthase () is an enzyme that catalyzes the chemical reaction:CoA-[4'-phosphopantetheine] + apo-acyl carrier protein formula_1 adenosine 3',5'-bisphosphate + holo-acyl carrier proteinThis enzyme belongs to the family of transferases, specifically those transferring non-standard substituted phosphate groups.
The systematic name of this enzyme class is CoA-4'-pantetheinephosphotransferase.
Other names in common use include acyl carrier protein holoprotein (holo-ACP) synthetase, holo-ACP synthetase, coenzyme A:fatty acid synthetase apoenzyme 4'-phosphopantetheine, transferase, holosynthase, acyl carrier protein synthetase, holo-ACP synthase, PPTase, AcpS, ACPS, acyl carrier protein synthase, P-pant transferase, and CoA:apo-[acyl-carrier-protein pantetheinephosphotransferase.
This enzyme participates in pantothenate and coa biosynthesis.  
Cytochrome c oxidase (COX), the terminal component of the mitochondrial respiratory chain, catalyzes the electron transfer from reduced cytochrome c to oxygen.
This component is a heteromeric complex consisting of 3 catalytic subunits encoded by mitochondrial genes and multiple structural subunits encoded by nuclear genes.
The mitochondrially-encoded subunits function in electron transfer, and the nuclear-encoded subunits may function in the regulation and assembly of the complex.
This nuclear gene encodes a protein which is not a structural subunit, but may be involved in the recruitment of copper to mitochondria for incorporation into the COX apoenzyme.
This protein shares 92% amino acid sequence identity with mouse and rat Cox17 proteins.
This gene is no longer considered to be a candidate gene for COX deficiency.
A pseudogene COX17P has been found on chromosome 13. 
An apoenzyme (or, generally, an apoprotein) is the protein without any small-molecule cofactors, substrates, or inhibitors bound.
It is often important as an inactive storage, transport, or secretory form of a protein.
This is required, for instance, to protect the secretory cell from the activity of that protein.
Apoenzymes becomes active enzymes on addition of a cofactor.
Cofactors can be either inorganic (e.g., metal ions and iron-sulfur clusters) or organic compounds, (e.g., flavin and heme).
Organic cofactors can be either prosthetic groups, which are tightly bound to an enzyme, or coenzymes, which are released from the enzyme's active site during the reaction.
Like any other plasma protein, levels drop in patients with hepatic disease due to reduced synthesizing capabilities.
Mechanisms of low ceruplasmin levels:   Gene expression genetically low (aceruloplasminemia)  Copper levels are low in general * Malnutrition/trace metal deficiency in the food source  Copper does not cross the intestinal barrier due to ATP7A deficiency (Menkes disease)  Delivery of copper into the lumen of the ER-Golgi network is absent in hepatocytes due to absent ATP7B (Wilson's disease) Copper availability doesn't affect the translation of the nascent protein.
However, the apoenzyme without copper is unstable.
Apoceruloplasmin is largely degraded intracellularly in the hepatocyte and the small amount that is released has a short circulation half life of 5 hours as compared to the 5.5 days for the holo-ceruloplasmin.
Mutations in the ceruloplasmin gene ("CP"), which are very rare, can lead to the genetic disease aceruloplasminemia, characterized by hyperferritinemia with iron overload.
In the brain, this iron overload may lead to characteristic neurologic signs and symptoms, such as cerebellar ataxia, progressive dementia, and extrapyramidal signs.
Excess iron may also deposit in the liver, pancreas, and retina, leading to cirrhosis, endocrine abnormalities, and loss of vision, respectively. 
1,10-Phenanthroline is an inhibitor of metallopeptidases, with one of the first observed instances reported in carboxypeptidase A. Inhibition of the enzyme occurs by removal and chelation of the metal ion required for catalytic activity, leaving an inactive apoenzyme.
1,10-Phenanthroline targets mainly zinc metallopeptidases, with a much lower affinity for calcium.