Write a 100-350 word essay about the enzyme human MPI. Provide information related to enzyme: i) function, ii) reaction pathways, ii) Location, and iv) diseases. In writing include these four subheadings

### Function
Human MPI, or mannose phosphate isomerase, is an enzyme crucial for carbohydrate metabolism. MPI catalyzes the interconversion of fructose-6-phosphate and mannose-6-phosphate, a key step in the production of GDP-mannose, which is essential for glycoprotein synthesis. This reaction is vital for the proper functioning of the glycosylation pathway, ensuring that cells have a sufficient supply of mannose derivatives needed for glycan formation.

### Reaction Pathways
MPI operates within the mannose metabolism and glycosylation pathways. The enzyme converts fructose-6-phosphate, a glycolysis intermediate, into mannose-6-phosphate. Mannose-6-phosphate is then used to generate GDP-mannose, which serves as a donor substrate for the synthesis of glycoproteins, glycolipids, and other mannose-containing glycoconjugates. This pathway is critical for the proper assembly and function of glycoproteins, which are involved in numerous cellular processes including cell-cell communication, immune response, and protein folding.

### Location
MPI is primarily localized in the cytoplasm, where it carries out its enzymatic function as part of the broader network of carbohydrate metabolism. The cytoplasmic location allows MPI to efficiently access its substrates, fructose-6-phosphate and mannose-6-phosphate, which are intermediates in glycolysis and glycosylation pathways. By interconverting these molecules, MPI plays a pivotal role in maintaining the balance of sugar nucleotides necessary for glycoprotein biosynthesis.

### Diseases
Mutations in the MPI gene cause a rare metabolic disorder known as congenital disorder of glycosylation type Ib (CDG-Ib). CDG-Ib is characterized by a deficiency in MPI activity, leading to insufficient production of GDP-mannose and, consequently, defective glycosylation. Symptoms of CDG-Ib include developmental delays, gastrointestinal issues, liver dysfunction, and hypoglycemia. Unlike many other congenital disorders of glycosylation, CDG-Ib can be treated with oral mannose supplementation, which bypasses the metabolic block caused by MPI deficiency. Understanding the function of MPI and its role in glycosylation is crucial for diagnosing and treating CDG-Ib, highlighting the enzyme's importance in cellular metabolism and human health.