9. SACCHARIDES: ALTERNATE ROUTES OF METABOLISM
441
HC = 0
I
HCOH
I
HOCH
I —
HCOH
I
HCOH
I
CH 2 OH
D-Glucose
HC = 0
I
HCOH
I
HOCH
—
I —
HCOH
I
HCOH
I
COOH
D-Glucuronic acid
COOH
I
HOCH
HOCH
HCOH
HOCH
O
II
c
I
HOC
HOC
►
I
HC
I
HOCH
I
CH 2 OH
CH 2 OH
L -Gulonic acid L -Ascorbic acid
CH=0
HCOH
CH 2 OP0 3 H ;
D-Xylulose-5-P
HOCH
HCOH
HCOH
CH 2 OH
L-Glucose
FIG. 5. Glucuronic acid pathway of glucose metabolism. After Eisenberg et al.
(U3).
In Section V phosphogluconate cleavage is measured by the appearance of C-1 of glucose in respiratory C0 2 , in excess of the yield from
C-6. C0 2 is also evolved in this heterolactic fermentation and, as in
phosphogluconate cleavage, carbon 6 is not recovered in respiratory
C0 2 . However, the processes differ in that other carbon atoms of glucose
are not concerned in C0 2 formation in the heterolactic fermentation.
Carbon atoms 2 and 3 form ethanol or acetic acid; transketolase appears
not to participate.