METABOLIC BIOCHEMISTRY

Summer 2005

Lecture 6

August 12, 2005

LNC Chapter 16

The Citric Acid Cycle

Krebs CycleTCA Cycle

From G. Perkins, C. Renken, M.E. Martone,S.J. Young, M. Ellisman, and T. Frey

Outer membraneInner membrane

Intermembrane spaceMatrix

Pyruvate dehydrogenase as seen by electronmicroscopy

E. coli enzyme:

Mass > 4.5x106

24 copies of transacetylase (E2)

24 copies of pyruvate dehydrogenase (E1)

12 copies of dihydro-lipoyl dehydrogenase

Pyruvate + CoASH + NAD+ acetyl-CoA + CO2 + NADH

E1

E3E2

LNC 16.3

Coenzyme A

LNC 16.14

Lipoamide

LNC Fig. 13-18

FAD/FMN

FADH2/FMNH2

Fig. 16.6

Figure from previous edition of LNC

TCA CYCLEKrebs cycleCitric acid

cycle

LNC 16.11

Products from one turn of the Krebs cycle

C4

C4

C4

C4

C6

C2

C5

C4

C6

LNC 16.8

Citrate Synthase

open form without substrates

closed from with substrates bound

oxaloacetate: yellowacetyl-coA: red

LNC 16.9 Iron-sulfur center in aconitase

X

Stereospecificity of the aconitase reaction

with citrate

LNC 16.14

LNC Fig.16.7

the only membrane-bound enzyme in the TCA cycle

LNC Fig.16.18

regulatory molecules:

NADHATP, ADPCa+2

key allosteric enzymes:

the dehydrogenasescitrate synthase

LNC Fig.16.15 the Krebs cycle is amphibolic

THE GLYOXYLATE CYCLE

LNC Chapter 16, pages 623-626

LNC Fig.16-20 Note that the figure 16-16 in the 3rd edition has an error(there is an O instead of an H)

C6

C6

C4

C4

C4C2C2

C2

from oxidation of fatty acids

LNC Fig.16.22

End of lecture 6August 12, 2005