Dehydration of Macromolecules I. Effect of Dehydration-Rehydration on Indoleacetic Acid Oxidase, Ribonuclease, Ribulosediphosphate Carboxylase, and Ketose-1-Phosphate Aldolase

Abstract

A pressure-membrane technique has been developed to physically manipulate the water potential of in vitro enzyme preparations. Enzyme preparations were subjected to a range of water potentials using this technique. Indoleacetic acid oxidase and ribonuclease activities were unaffected by changes in water potential. Ribulosediphosphate carboxylase was sensitive to water potential change and its activity was reduced to 20 % of controls at a water potential of -14 bars. Loss of activity was attributed to fragmentation of the molecules to an apparent molecular weight of less than 1500. Ketose-1-phosphate aldolase lost all activity when subjected to slight water potentials (-1 bar) and fragmented in a similar fashion to ribulosediphosphate carboxylase. Fragmentation in both cases was not due to protease activity. It is concluded that water has an important structural role in maintaining the molecular integrity of ribulosediphosphate carboxylase and ketose-1-phosphate aldolase, but not in indoleacetic acid oxidase and ribonuclease.

Salinity Induced Changes in Peroxidase Activity in the Green Seaweed Ulva lactuca

“…The formation of isoenzymes occurs during frost hardening (Roberts 1969). Inhibition of several enzymes occurs under stress conditions (Bardzik et al 1971, Darbyshire andSteer 1973). Differential inhibition of peroxidases in drought resistant and sensitive varieties of Zea mays L. was documented by Thakur et al (1981) and Mali and Mehta (1977 a, b).…”

The Effects of Shoot Water Status on Some Photosynthetic Partial Processes in Sitka Spruce

“…The decline in both cyclic and non-cyclic photophosphorylation in sunflower from their maximum rates at -12 bar to zero at -17 bar were the only processes which could explain the eventual decline in F^ in vivo to zero (Keck and Boyer 1974), This may be of similar importance in Sitka spruce, particularly if non-membrane components required for phosphorylating activity become limiting at low V, However, so far photophosphorylation has not been measured in Sitka spruce or otber conifers, RuDP carboxylase is associated with the stroma and is a membrane protein. The activity of soluble spinach ribulose 1,5-diphosphate carboxylase was reduced to 20% of the control rate at a water potential of -14 bar in a pressuremembrane chamber (Darbyshire and Steer 1973), Much smaller reductions in activity were observed when the enzyme was isolated in vitro on the chloroplast membrane in spinach in a sorbitol solution of approximately the same osmotic potential (Plaut 1971), and after extraction from the chloroplast in cotton (Jones 1973), pea seedlings (Lee et al 1974) and wheat and barley (Johnson et al 1974), The resistance of the chloroplast membranes to disruption under severe water stress in vivo may prevent the disintegration of the enzyme at low V and explain the retention of high activities in vitro in Sitka spruce even below -30 bar when the needles were severely desiccated. Alternatively, if conformational changes had occurred on the membrane in vivo (Plaut 1971), the enzyme may have reverted to its carboxylating form in the in vitro assay.…”

Some Aspects of Carbon Metabolism and Translocation in Onions

“…Ribulose bisphosphate (RuBP) carboxylase was assayed in tricine buffer homogenates by the radioisotope procedure described in Darbyshire and Steer (1973).…”