Ewing E E, Devlin M, McNeill D A, McAdoo M H, Hedges A M
Department of Vegetable Crops, Cornell University, Ithaca, New York 14853.
Plant Physiol. 1977 May;59(5):925-9. doi: 10.1104/pp.59.5.925.
The increase in the invertase activity of extracts from freshly cut potato (Solanum tuberosum L.) by "foaming," caused by selective denaturation of an endogenous invertase inhibitor, did not occur in extracts made from thin disks 2 days after slicing. Rather, foaming such extracts decreased invertase activity. Apparently, the inhibitor disappeared after slicing, and the enzyme became more labile to foaming. Such disappearance of inhibitor could account for up to 15% of the dramatic increase in total invertase activity that had occurred within 2 days after slicing. The difference between extracts from 0-day and 2-day slices was mainly in the first of two peaks of invertase activity eluted from diethylaminoethyl-cellulose columns. This peak was increased by foaming 0-day extracts, but even when foamed was much smaller than in 2-day extracts. The apparent loss in inhibitor was not caused by a decreasing susceptibility of the enzyme to the inhibitor. Both the increase in total invertase activity and the apparent loss of inhibitor after slicing were partially blocked by actinomycin D and completely blocked by cycloheximide.The presence of the inhibitor can lead to serious errors in the usual whole disk method of assay for invertase in slices. Ethyl acetate treatment reduces the solubility of the enzyme but does not inactivate the inhibitor.
新鲜切割的马铃薯（Solanum tuberosum L.）提取物中，因内源性转化酶抑制剂的选择性变性而通过“发泡”导致的转化酶活性增加，在切片2天后从薄片制备的提取物中并未出现。相反，对这类提取物进行发泡会降低转化酶活性。显然，抑制剂在切片后消失，且酶对发泡变得更不稳定。抑制剂的这种消失可解释切片后2天内总转化酶活性急剧增加的高达15%。0天和2天切片提取物之间的差异主要在于从二乙氨基乙基纤维素柱洗脱的转化酶活性的两个峰中的第一个。通过对0天提取物进行发泡，这个峰增加了，但即使发泡后也比2天提取物中的小得多。抑制剂的明显损失并非由酶对抑制剂的敏感性降低所致。切片后总转化酶活性的增加和抑制剂的明显损失均部分被放线菌素D阻断，并被环己酰亚胺完全阻断。抑制剂的存在会在通常的切片中转化酶全片测定方法中导致严重误差。乙酸乙酯处理会降低酶的溶解度，但不会使抑制剂失活。
