ACP1GUA-1--a low-activity variant of human erythrocyte acid phosphatase: association with increased glutathione reductase activity.

ACP1GUA-1, a variant of human erythrocyte acid phosphatase, exists as a polymorphism (allele frequency of .132) in the Guaymi Indians of Central America. This variant has an electrophoretic mobility similar to the common B- and C-type variants, but individuals of the ACP1GUA-1 phenotype have a level of enzyme activity only 27% of the activity expected for the ACP1C variant. The GUA-1 variant is more thermostable than is the B variant, and the order of responsiveness to the modulation of activity by purine analogs and folate is always (B)-(A)-(GUA-1). Thus, the GUA-1 variant is a low-activity variant with C-like regulatory properties. Erythrocytes from individuals of the ACP1GUA-1 phenotype have increased basal levels of glutathione reductase, and a larger fraction of the glutathione reductase protein is present as the holoenzyme, indicating increased levels of flavin adenine dinucleotide in the erythrocytes of these individuals. This is consistent with the suggestion that ACP1 has a physiological function as a flavin mononucleotide phosphatase.