Artifacts in Intracellular Enzyme Distribution Caused by Alkaline Homogenates

Abstract

Many papers report the simultanieous occurrence of the same enzymes in several subcellular fractions from planits. Isocitrate dehvdrogenase was observed in the mitochondrial and the soluble fraction from lettuce !(7) and peas (3), and these 2 fractions from apples both contained malic enzyme (5). Glucose-6-P dehydrogenase was recorded in these 2 fractions from lettuce (6), carrot )(4) and pea (9 Table I shows the shift from the particle fraction to the soluble fraction of the enzymes, convertinig glvcerate 3-P into malate. by a non-leakable inhibitory substance, present in the particle fraction (The purification of these enzymes is in progress and points to the presence of suclh anl inhibitory substance). The same procedure, applied to spinach leaves resulted in the sanme phenomenon. Glucose-6-P dehydrogenase and isocitrate dehydrogenase activities in mitochondria, isolated from a Basic comllpositioni of the grinding mediunm was 0.35 m sucrose, 5 ni-m EDTA, 5 mai 3-mercaptoethanol and 2 % (w/v) bovine aibumini (pH 7.0). Two ml of grinding mediumi per g of leaves were used. The leaves were ground in a mortar with sanid. The pH of the homogenates was recorded, honmogenates were purified by straining througlh 4 layers of cheeseclotlh and 1 min 200 g centrifugation. Particles w-ere separated from the soluble fraction by 20 Imii 14,000 g. In the assays the enizymes in the particle fraction were totally solubilized by suspending in TWEEN. Phosphoglyceroinutase + enolase + PEP-carboxylase + malate deyhdrogenase activities were measured in the 2 fractions as described previously (2).

Subcellular Localization of Zinc and Calcium in Bean (Phaseolus vulgaris L.) Tissues

“…There was a much greater proportion of the absorbed "Zn localized in root mitochondria and nuclei of the zinc-sensitive Sanilac than in the zinc-tolerant Saginaw. Stem The intracellular localization of enzymes in plant tissues has received wide attention (2,4,6,8,11,15,16,18,20 …”