inositol-3-phosphate synthase (myo-inositol-1-phosphate synthase, MI-1-P synthase, MIP synthase, hIPS, myo-inositol 1-phosphate synthase A1, hINO1, INO1, ISYNA1)

Function

• key enzyme in myo-inositol biosynthesis pathway that catalyzes the conversion of glucose 6-phosphate to 1-myo-inositol 1-phosphate in a NAD-dependent manner
• rate-limiting enzyme in the synthesis of all inositol- containing compounds
• inhibited by mood-stabilizing drugs such as valproate & lithium
• polyol metabolism; myo-inositol biosynthesis
• myo-inositol from D-glucose 6-phosphate: step 1/2

D-glucose 6-phosphate <--> 1D-myo-inositol 3-phosphate

Cofactor: NAD

Kinetic parameters:

• KM=0.57 mM for 6-phosphate
• KM=8 uM for NAD
• Optimum pH is 8.0

Structure

• belongs to the myo-inositol-1-phosphate synthase family

Compartment

cytoplasm (putative)

Alternative splicing

named isoforms=2

Expression

• highly expressed in testis, ovary, heart, placenta & pancreas
• weakly expressed in blood leukocyte, thymus, skeletal muscle & colon
• induced by glucose & lovastatin
• up-regulation is prevented by mevalonic acid, farnesol, & geranylgeraniol
• up-regulated by E2F1

More general terms

• isomerase

Database

• Kegg: http://www.genome.jp/dbget-bin/www_bget?hsa:5147
• UniProt: http://www.uniprot.org/uniprot/Q9NPH2.html