Glycolytic enzymes in polyamine-treated bovine retina

The retina is characterized by glycolysis under aerobic conditions, mediate d by lactate dehydrogenase isoenzyme-5 (LDH-5) as well as by the soluble is oenzyme of malate dehydrogenase. Bovine retina LDH and MDH isoenzymes and t heir activities were studied after polyamine treatment. Our results showed that LDH-5 isoenzyme presented the highest activity in untreated as well as in putrescine-treated retina. Decreased activity was present when the reti na was treated with spermidine or spermine. It was demonstrated that retini c LDH-5 had a high affinity for lactate which enabled the isoenzyme to be m ore effective than the other LDH isoenzymes in the conversion of NADH to NA D. Therefore, the putrescine enhancing LDH-5 activity appeared to be capabl e of stimulating NAD-mediated rhodopsin regeneration. Putrescine induced a marked increase of both MDH isoenzymes - soluble (s-MDH) and mitochondrial (m-MDH), while spermine and spermidine mostly affected the soluble form of the enzyme. Putrescine induced a three-fold increase in s-MDH and m-MDH act ivities, while spermine and spermidine induced a foul to five-fold increase in s-MDH. These results document the differential effects of polyamine tre atment on LDH and MDH isoenzyme activities.