Gout Is A Metabolic Disorder Of Purine Catabolism

Various genetic defects in PRPP synthetase (reaction 1, Figure 34-2) present clinically as gout. Each defect— eg, an elevated Vmax, increased affinity for ribose 5-phosphate, or resistance to feedback inhibition—results in overproduction and overexcretion of purine catabo-lites. When serum urate levels exceed the solubility limit, sodium urate crystalizes in soft tissues and joints and causes an inflammatory reaction, gouty arthritis. However, most cases of gout reflect abnormalities in renal handling of uric acid.

Figure 34-8. Formation of uric acid from purine nucleosides by way of the purine bases hypoxanthine, xanthine, and guanine. Purine deoxyribonucleosides are degraded by the same catabolic pathway and enzymes, all of which exist in the mucosa of the mammalian gastrointestinal tract.

ho-h2c

OH oh Adenosine

ho-h2c

h2n^n^n ho-h2c

HU-7H Oh Oh

Inosine

OH OH Guanosine

Ribose 1-phosphate

-NH Hypoxanthine lOc")

-NH Hypoxanthine h2o

N' ^NH Guanine

H2O2 O

H2O2 O

Uric acid

Uric acid h2o

OTHER DISORDERS OF PURINE CATABOLISM

While purine deficiency states are rare in human subjects, there are numerous genetic disorders of purine ca-tabolism. Hyperuricemias may be differentiated based on whether patients excrete normal or excessive quantities of total urates. Some hyperuricemias reflect specific enzyme defects. Others are secondary to diseases such as cancer or psoriasis that enhance tissue turnover.

Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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