Q.14 Glycerol kinase is not expressed in

1. adipose tissue

2. liver

3. kidney

4. heart

Glycerol kinase is absent in adipose tissue, making it the correct answer to this biochemistry question on tissue-specific enzyme expression.

Why Adipose Tissue?

Adipose tissue lacks glycerol kinase activity, preventing glycerol from lipolysis of triacylglycerols (TAGs) from being reused for re-esterification or entry into gluconeogenesis. This design favors fat storage: free fatty acids are released into blood for other tissues, while glycerol exits unmetabolized, avoiding a futile TAG cycle. Consequently, adipocytes depend on glucose-derived glycerol-3-phosphate (via DHAP) for TAG synthesis during lipogenesis.

Liver Expression

Liver expresses high glycerol kinase levels, enabling glycerol phosphorylation to glycerol-3-phosphate for gluconeogenesis or lipid synthesis. This supports fasting glucose production from absorbed glycerol. GK deficiency here leads to hyperglycerolemia, confirming its key role.

Kidney Expression

Kidney shows glycerol kinase activity, aiding glycerol utilization for energy or gluconeogenesis, similar to liver. It handles plasma glycerol clearance alongside hepatic uptake.

Heart Expression

Heart expresses glycerol kinase, using glycerol-3-phosphate for phospholipid synthesis and energy metabolism under stress. GK knockout reduces cardiac lipids, indicating reliance on glycerol pathways.​