Changes in cystathionine gamma-lyase levels in rat liver during lactation

Rat liver cystathionine gamma-lyase activity increased rapidly with the onset of lactation, reaching a maximum value at week 2 and slowly decreasing thereafter. In non-lactating rats, from which the litters had been removed on the day of birth, the activity of this enzyme increased only minimally. The enzyme activity in the presence and absence of pyridoxal 5'-phosphate (PLP) did not differ significantly, indicating that the cystathionine gamma-lyase in lactating rat liver was also saturated with PLP as control rat. We then investigated whether the increased activity was caused by increases in the enzyme concentration. An antibody, prepared form purified rat liver cystathionine gamma-lyase was utilized for the detection of enzyme content by immunoblot analysis and enzyme immunoassay. On immunoblot analysis, this antibody stained purified cystathionine gamma-lyase, as well as staining a single polypeptide from liver cytosolic proteins that co-migrated with the purified enzyme at about 40 kDa. Changes in the staining intensity of the antibody paralleled the activity of the enzyme. The enzyme immunoassay showed that the content of liver cystathionine gamma-lyase at weeks 0, 1, 2 and 5 of lactation was 1.67, 2.33, 5.19, and 2.17 mg per g of liver, respectively, whereas in the non-lactating rats, the enzyme concentration at week 2 was found to be 2.20 mg per g of liver. The changes in enzyme concentration detected by enzyme immunoassay were also consistent with enzyme activity. We concluded that the increased cystathionine gamma-lyase activity in the lactating rat liver was a result of an increase in enzyme concentration.