代谢
L-刀豆氨酸(CAV)是从杰克豆(Canavalia ensiformis)中分离出来的精氨酸(ARG)类似物。CAV被整合到MIA PaCa-2人类胰腺癌细胞中的细胞蛋白中,异常的刀豆氨酰蛋白并未优先降解。刀豆氨酸通过精氨酸酶介导的水解裂解为刀豆宁(CAN)和尿素。CAN是一种强效代谢物,能够使含有维生素B6的酶失活,并可能抑制细胞生长。为了确定MIA PaCa-2细胞中精氨酸酶的存在及其对ARG和CAV的特异性,采用了一种放射性分析,该分析通过量化由精氨酸酶介导的L-[胍基-(14)C]ARG或L-[胍基氧-(14)C]CAV水解裂解时释放的(14)C来进行。当细胞暴露于[(14)C]CAV或[(14)C]ARG时,释放的(14)CO2量微不足道。胰腺癌细胞分泌的精氨酸酶量极少。比较了CAN和CAV在不同ARG浓度下对细胞的细胞毒性影响。这些研究表明,CAV对MIA PaCa-2细胞的细胞毒性效应不能归因于转化为活性代谢物CAN。精氨酸酶对CAV的水解较慢且减少,使得CAV能够持续存在,并增加了其整合到这些细胞蛋白中的机会。胰腺中缺乏大量的精氨酸酶使得CAV成为胰腺癌进一步研究的值得候选物。
L-Canavanine (CAV) is an arginine (ARG) analog isolated from the jack bean, Canavalia ensiformis. CAV becomes incorporated into cellular proteins of MIA PaCa-2 human pancreatic cancer cells and the aberrant, canavanyl proteins are not preferentially degraded. Hydrolytic cleavage of CAV to canaline (CAN) and urea is mediated by arginase. CAN is a potent metabolite that inactivates vitamin B6-containing enzymes and may inhibit cell growth. To determine the presence of arginase and its specificity for ARG and CAV in MIA PaCa-2 cells, a radiometric assay, which quantifies the (14)C released from the hydrolytic cleavage of L-[guanidino-(14)C]ARG or L-[guanidinooxy-(14)C]CAV mediated by arginase, was employed. Insignificant amounts of (14)CO2 were released when cells were exposed to [(14)C]CAV or to [(14)C]ARG. Pancreatic cancer cells secrete a negligible amount of arginase. Cytotoxic effects of CAN and CAV were compared on cells exposed to varying concentrations of ARG. These studies provide evidence that CAV's cytotoxic effects on MIA PaCa-2 cells cannot be attributed to conversion to the active metabolite CAN. A slower and decreased hydrolysis of CAV by arginase allows CAV to persist and increases its chances of incorporating into proteins in these cells. Lack of considerable amounts of arginase in the pancreas makes CAV a worthy candidate for further studies in pancreatic cancer.
来源:Hazardous Substances Data Bank (HSDB)