Phosphoglucose isomerase isozymes and allozymes of the brown trout, Salmo trutta L

1. In brown trout the Pgi-1 and Pgi-2 loci are predominantly expressed in white skeletal muscle; Pgi-3 being mainly expressed in most other tissues. 2. Total PGI activity determinations revealed that the allele formerly designated Pgi-2(65) is a null allele, Pgi-2(n). 3. Enzyme kinetic studies on the partially purified PGI homodimeric isozymes revealed that from 5 to 25 degrees C both PGI-1 and PGI-2 had significantly higher mean Km(F6P) values compared to PGI-3. 4. Distinct metabolic roles for the "muscle" (PGI-1, PGI-2) and "liver" (PGI-3) isozymes are proposed. 5. Significant Km (F6P) differences were found among the PGI-2 allozymes and among the PGI-3 allozymes.