Enzyme patterns in trisomy 19 of the mouse

Activity patterns of cytosolic and mitochondrial enzymes of carbohydrate and amino acid metabolism have been measured in murine trisomy 19. In spite of marked hypoplasia, no significant alterations of the patterns (per gram of organ weight) were observed, with the exception of glutamate oxaloacetate transaminase (GOT‐1), and phosphoglycerate mutase (PGAM). Clear‐cut gene dosage effects in liver, brain, heart, skeletal muscle, and erythrocytes of fetal and newborn mice, confirm the assignment of GOT‐1 to chromosome 19. Data obtained for PGAM demonstrate that one of the two different subunits leading to organ‐specific isozyme patterns of the dimer enzyme protein is coded on chromosome 19 (gene Pgam‐1). Dosage effects are fully expressed in liver, brain, and erythrocytes (AA‐type isozyme), but not in skeletal muscle (BB‐type isozyme). Dosage effects on the hybrid AA‐AB‐BB‐isozyme pattern in the course of development of the heart muscle, were demonstrated by means of quantitative activity measurement after electrophoretic separation. The comparison of enzyme patterns of eusomic and trisomic erythrocytes, produced after injection of fetal stem cells into irradiated adult carriers (transplantation chimaeras), revealed enzyme activity ratios that were similar to those produced by erythrocytes of adult euploid and trisomic mice. This is in agreement with the chromosome assignments and dosage effects mentioned above.