Differential regulation of XXXX synthesis and transmethylation reactions in methylthioadenosine phosphorylase deficient @entity1 cells.

@entity1 @entity851 @entity1255 @entity19 @entity6546 @entity13710 @entity5784 @entity7726 @entity8641 @entity4664
The consumption of @entity7726 during @entity4664 synthesis and transmethylation reactions yields stoichiometric amounts of @entity8641 and @entity13710 , respectively. Information concerning the regulation of the two routes of @entity7726 metabolism in viable cells under changing growth conditions is limited. The present experiments have measured the time-dependent accumulation of @entity8641 and @entity5784 in the medium of four malignant @entity1 and @entity19 cell lines deficient in @entity8641 phosphorylase ( @entity8641 : @entity6546 methylthioribosyltransferase). Included in this group were anchorage-independent and anchorage-dependent cells. The enzyme-deficient cells did not detectably cleave @entity8641 , and did not appreciably metabolize @entity1255 . A comparison of @entity8641 and @entity1255 excretion therefore provided a noninvasive method for estimating the relative rates of @entity4664 synthesis and transmethylation. Early after the release of @entity1 CEM lymphoblasts from density dependent @entity851 , @entity8641 production increased, and exceeded @entity1255 synthesis. @entity8641 formation reached a maximum of 0.9 nmol/12 h per 10(6) cells prior to the onset of exponential growth. The kinetics of @entity1255 synthesis were different. @entity1255 accumulation was proportional to the specific growth rate, and achieved a peak of 3.1 nmol/12 h per 10(6) cells during mid-exponential phase, at which time @entity8641 production was falling. Similar patterns of @entity8641 and @entity1255 excretion were observed in other @entity8641 phosphorylase deficient cell lines. These data show that @entity4664 synthesis and transmethylation are differentially regulated during the growth cycle of @entity1 cells.
