1. PENTOSE PHOSPHATE CYCLE
3
will be discussed later.] This cycle (Fig. 2) starts with the reaction of
carbon dioxide with a pentose diphosphate to form three-carbon phosphorylated acids. This three-carbon compound is subsequently reduced
to triose phosphate, which then condenses with another molecule of
HC=0
HCOH
HOCH
HCOH
HCOH
HgCOH
GLUCOSE
HEXOKINASE
HC=0
HCOH
G-6-P
H 2 CO®
R-5-P
FIG. 1. The oxidative pentose phosphate cycle.
triose phosphate to form a hexose diphosphate. The latter undergoes a
series of rearrangements and transformations to form, finally, the carbon
dioxide acceptor ribulose-l,5-diphosphate. In the course of this cycle,
adenosine triphosphate (ATP) and reduced triphosphopyridine nucleotide (TPNH) are consumed.