Before the carbonyl was converted to the alcohol, there were two
bonds to oxygen, one bond each to other carbons, or in the case of
the aldehyde, one to carbon and one to hydrogen, total 4 bonds. After
the conversion, there is one bond to oxygen, and an additional
bond to hydrogen, total 4 bonds. There is therefore no
change in the oxidation state of the carbon.
Here is a database of enzyme reaction mechanisms:
http://www.ebi.ac.uk/thornton-srv/databases/MACiE/
If you type in dehydrogenase in the top box of the search, you get
a list of enzymes. If you click on one of the enzymes in the list
you get a detailed description of the mechanism.
For malonate dehydrogenase:
http://www.ebi.ac.uk/thornton-srv/databases/cgi-bin/MACiE/getPage.pl?id=M0021
"Step 1 Asp278 deprotonates Lys183, which deprotonates the hydroxyl group of malate,
which eliminates a hydride ion that is added to NADP.
Step 2 The reduced intermediate decarboxylates with concomitant double bond rearrangement.
Step 3 The oxyanion collapses, reducing the C=C with concomitant deprotonation of Tyr112.
Step 4 Tyr112 deprotonates Lys183 which deprotonates Asp278 in an inferred return step."
Note the deprotonation (protonation going the other way):
"Asp278 deprotonates Lys183, which deprotonates the hydroxyl group of malate,
which eliminates a hydride ion that is added to NADP."
"Tyr112 deprotonates Lys183 which deprotonates Asp278 in an inferred return step."
No solvent is involved, protonation/deprotonation occurs via donation/acceptance
from the amino acid residues (aspartic acid, lysine and tyrosine in this case).
This is the general way that all of these types of enzyme reactions work.
I don't know if you are misunderstanding, misquoting (deliberately or not)
or simply making up those textbook quotes, but they are wrong. Given that
you've misunderstood molality in another thread, written incorrect stoichiometry
and structures in this one, and don't understand the oxidation state of
carbon in organic molecules (see above), I'm afraid I can't trust what you are saying.
You seem to be trying to "win" this argument, but it's a waste of time
and therefore I'm bowing out. I've provided enough online references
from reputable sources for you to figure this out.
Ray