Stability of mammalian lens phosphofructokinase

Two interconvertible phosphofructokinase (PFK) forms were found in rat and human lenses; whereas only one predominant form was found in calf lens. PFK isolated from these lenses possessed a common property, i.e., pH-dependent cold (or acid) lability. The inactivation was prevented by including either adenosine triphosphate (ATP) or fructose-6-phosphate (fru-6-P) in the incubating media. The protective effect of ATP or fru-6-P was complete in rat or calf lenses. In human lens, although fru-6-P was fully protective, ATP protected only partially. The inactivation could be reversed by addition of fru-6-P, but not ATP, to the incubating media at 37.5 degrees C. Lens organ culture studies showed that the depletion of lenticular ATP seemed to precipitate the loss of PFK.