ribulóz

Ribulóz, also known as ribulose in chemical notation, is a five-carbon sugar of the ketose class. It exists in two enantiomeric forms, D- and L-, with the D form predominating in nature. In its linear form, ribulose has a ketone group at the second carbon.

In aqueous solution ribulose can cyclize to form ring structures, most commonly a five-membered furanose form, with other cyclic forms being much less common. Like other sugars, ribulose can exist in equilibrium between its linear and cyclic forms and can participate in mutarotation and tautomerization under certain conditions.

Biological significance: Ribulose-5-phosphate is a central metabolite of the pentose phosphate pathway, produced from ribose-5-phosphate by isomerase and then converted to xylulose-5-phosphate by epimerase. This pathway provides ribose-5-phosphate for nucleotide synthesis and generates NADPH for reductive biosynthesis and antioxidant defense. Ribulose derivatives thus link carbohydrate metabolism with nucleotide biosynthesis and redox balance.

In photosynthetic organisms, related compounds are involved in carbon fixation: ribulose-1,5-bisphosphate (RuBP) is the substrate for the enzyme RuBisCO in the Calvin cycle. While ribulose itself is not the direct substrate in this cycle, its phosphorylated derivatives are chemically connected to the cycle’s intermediates.

Ribulóz occurs naturally in organisms that utilize pentose phosphate metabolism and can be produced synthetically. In carbohydrate chemistry, ribulose serves as a reference sugar for testing reactions and for studying the properties of ketopentoses.