Draw the mechanism of hydride transfer in a NAD+-dependent dehydrogenase that interconverts alcohols and ketones!
examples: alcohol DH, glycerinaldehyde-3-phosphate DH
Draw the chemical structure of the nicotinamide ring of NAD(P)+ in the oxidized and reduced NAD(P)H state!
Draw the chemical structures of substrate classes of thiamine enzymes and indicate which bonds are susceptible to cleavage by thiamin!
More specifically:
alpha-keto acids
vicinal diketones
alpha-hydroxy ketones
Is hydride transfer in NAD+-dependent dehydrogenases stereospecific? Explain the underlying mechanism and suggest an experiment that can prove or rule out stereospecific hydride transfer!
Yes, hydride transfer in NAD+-dependent enzymes is stereospecific.
architecture of active site is responsible
Experiment: Monodeuterated NADH (1D, 1H) used for reaction. Are products deuterated, undeuterated or a mixture?
Alternative: Deuterated substrate is used, NADH is checked for stereoisomeries
Draw the chemical structure of the central carbanion-enamine intermediate in thiamin enzymes and name two possibilities how reaction can progress from this state!
Draw the chemical structure of the pyruvoyl “cofactor” and name a reaction where this cofactor is acting!
CH3-CO-CO-NH~Enzyme
pyruvoyl decarboxylase: decarboxylation of histidine
Draw mesomeric structures of the alpha-carbanion derived upon PLP-assisted decarboxylation!
What are quinoproteins? Name two classes of these and the reactions they are typically catalyzing!
quinoproteins: enzymes with o-quinone prosthetic group
PQQ: pyrroloquinoline quinone
bacterial alcohol DH:
alcohol ⇌ aldehyde
TPQ: topaquinone
copper amine oxidases:
RCH2NH2 + H2O + O2 ⇌ RCHO + NH3 + H2O2
Draw the chemical structure of thiamine diphosphate and mark the reactive atom! Why is that particular atom so reactive?
(“Kai’s favorite topic”)
H can be cleaved, remaining negative charge is quite stable because of delocalization and can attack nucleophilically
Name the two half-reactions typically catalyzed by flavoenzymes and provide an example!
Draw the structure of the biotin cofactor in resting and “cargo-loaded” state! Explain how cargo (substrate) is chemically activated in biotin enzymes?
long “arm” is normally attached to lysine in the enzyme and can move substrate around
activation of substrate (in this case: carboxy-group) first by phosphorylation, then by binding to biotin (makes carboxy-C more electrophilic?)
Draw the chemical structure of PLP in covalent linkage with an alpha-amino acid for a PLP i) decarboxylase and ii) racemase!
Draw the isoalloxazine ring system of flavin cofactors in the oxidized and two-electron reduced state!
(special about flavin: In contrast to NAD+, for example, flavin can accept one or two single electrons, not only hydrides)
Zuletzt geändertvor 23 Tagen
