Nitrogen metabolism in goldfish, Carassius auratus (L.) : Activities of transamination reactions, purine nucleotide cycle and glutamate dehydrogenase in goldfish tissues

Abstract

1. 1. The capacity of homogenates of goldfish lateral red muscle, dorsal white muscle and liver to transaminate several amino acids with α-ketoglutarate has been examined. 2. 2. Active transamination was observed with aspartate in dorsal white muscle, with aspartate and branched-chain amino acids in lateral red muscle, and with alanine, aspartate, branched-chain amino acids, histidine, and tyrosine in liver. 3. 3. The existence of glutamate dehydrogenase and a complete purine nucleotide cycle could be demonstrated. 4. 4. In muscle tissues the activities of GlDH* and the purine nucleotide cycle are of the same order, while in liver GlDH activity exceeds that of the purine nucleotide cycle with two orders of magnitude. 5. 5. Both pathways for amino acid deamination have sufficient capacity to be responsible for observed ammonia production rates of goldfish. 6. 6. From my data it is likely that the purine nucleotide cycle is operating as a “futile cycle” spinning at a rate which approaches the maximum flux through adenylosuccinatesynthetase.