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Bound hydroxyproline excretion following gelatin loading in prolidase deficiency
Insights
Patients with prolidase deficiency excrete significantly more peptide-bound hydroxyproline after gelatin loading, indicating impaired hydrolysis. This highlights the crucial role of prolidase in processing hydroxyproline-containing peptides.
Area of Science:
- Biochemistry
- Human Physiology
- Genetics
Background:
- Prolidase is an enzyme crucial for the hydrolysis of dipeptides containing proline.
- Deficiency in prolidase leads to an accumulation of peptide-bound hydroxyproline.
- Understanding hydroxyproline metabolism is important for diagnosing and managing related disorders.
Purpose of the Study:
- To evaluate peptide-bound hydroxyproline excretion in individuals with prolidase deficiency and heterozygotes.
- To assess the impact of gelatin loading on hydroxyproline excretion in different subject groups.
- To elucidate the role of prolidase in the intestinal absorption and hydrolysis of hydroxyproline.
Main Methods:
- Assessing peptide-bound hydroxyproline excretion before and after gelatin loading.
- Comparing excretion patterns in children and adults with prolidase deficiency, heterozygotes, and normal controls.
- Quantifying the ingested hydroxyproline load and its subsequent excretion over 24 hours.
Main Results:
- Prolidase deficiency patients excreted 6.9-24 times more bound hydroxyproline than controls.
- Following gelatin loading, homozygotes excreted 14.4-17.3 times more ingested hydroxyproline than normal children.
- A significant portion of ingested hydroxyproline was excreted unhydrolyzed in prolidase deficiency patients.
Conclusions:
- Prolidase deficiency leads to substantial unhydrolyzed peptide-bound hydroxyproline crossing the intestinal wall.
- Prolidase plays a vital role in the normal hydrolysis of peptide-bound hydroxyproline.
- The study underscores the diagnostic utility of hydroxyproline excretion tests in prolidase deficiency.
Abstract:
The excretion of peptide-bound hydroxyproline before and after gelatin loading was evaluated in two children with prolidase deficiency, two adult heterozygotes, and normal controls. On a low hydroxyproline diet, the patients with prolidase deficiency excreted 6.9 and 2.4 times more bound hydroxyproline than normal children. The bound hydroxyproline excretion for the heterozygotes was comparable to the adult controls. Children ingested 20 g of gelatin and adults 29 g. In the 24 hr following gelatin loading, the homozygotes excreted 14.4 and 17.3 times more of the ingested load of hydroxyproline than did normal children. This constituted 39% and 47% of the hydroxyproline ingested. Of the hydroxyproline excreted in 24 hr, 58%, and 61.4% was excreted in the first 6 hr. Over the 24 hr period, the normal children excreted 2.7% of the hydroxyproline ingested (97.8% in the first 6 hr). The heterozygotes excreted only slightly more than the adult controls. The normal adults excreted 6.0% of the ingested hydroxyproline (82.8% in the first 6 hr). In prolidase deficiency, large amounts of peptide-bound hydroxyproline can cross the intestinal wall unhydrolyzed. Prolidase appears to have an important role in normal hydrolysis of peptide-bound hydroxyproline.