Davidson S J
Biochim Biophys Acta. 1975 Dec 5;411(2):282-90.
Degradation of exogenous [125I] ribonuclease by renal lysosomes follows first-order kinetics in ribonuclease concentration. To demonstrate this, it was necessary to apply corrections for the presence of labeled but digestively inactive particles, either pinocytic vesicles or lysosomes damaged during preparation. Such kinetics were not observed under conditions favoring lysosomal breakdown, i.e., in isotonic KCl, or in the absence of EDTA. The kinetic analysis allows determination of half-times for lysosomal protein digestion. This facilitates comparison of different lysosome preparations, or of in vitro degradation rates with results of in vivo metabolism studies. Degradation of [125I] ribonuclease showed a half-time of about 11 1/2 minutes in isotonic sucrose or saline media. This is less than the half-time for decrease of kidney radioactivity in vivo after uptake of [125I] ri-onuclease. The proportion of exogenous, labeled protein contained within secondary lysosomes was determined as a function of time after injection of ribonuclease, to monitor transfer of the protein from pinocytic vesicles to lysosomes. Ribonuclease molecules remained in pinocytic vesicles for approximately three minutes after uptake, before passage into the lysosomes.
肾溶酶体对外源[125I]核糖核酸酶的降解在核糖核酸酶浓度方面遵循一级动力学。为了证明这一点，有必要对标记但无消化活性的颗粒（即吞饮小泡或制备过程中受损的溶酶体）的存在进行校正。在有利于溶酶体破裂的条件下，即在等渗KCl中或在没有EDTA的情况下，未观察到这种动力学。动力学分析允许确定溶酶体蛋白消化的半衰期。这便于比较不同的溶酶体制备物，或体外降解率与体内代谢研究结果。在等渗蔗糖或盐溶液培养基中，[125I]核糖核酸酶的降解显示半衰期约为11.5分钟。这比摄取[125I]核糖核酸酶后体内肾脏放射性降低的半衰期要短。在注射核糖核酸酶后，测定次级溶酶体内所含外源标记蛋白的比例，以监测蛋白质从吞饮小泡向溶酶体的转移。摄取后，核糖核酸酶分子在吞饮小泡中保留约三分钟，然后进入溶酶体。
