Light-induced changes in the distribution of the 36000-Mr polypeptide of NADPH-protochlorophyllide oxidoreductase within different cellular compartments of barley (Hordeum vulgare L.)

Changes in the relative content of NADPH-protochlorophyllide oxidoreductase during the light-induced greening of barley plants were measured both in the total leaf extract as well as in intact and broken plastids. The enzyme protein was identified by its apparent molecular weight and its immunological crossreactivity with an antiserum directed against the NADPH-protochlorophyllide oxidoreductase. The monospecificity of the antiserum was tested by two different criteria: i. The antiserum was purified by affinity chromatography. ii. It was demonstrated that the antiserum crossreacts with only those polypeptides which appear to be enzymatically active. In the fraction of broken plastids isolated from leaves of briefly illuminated barley plants the concentration of the enzyme protein was reduced drastically. Our results indicate that this decrease in enzyme protein content is the consequence of an artificial proteolytic breakdown of the membrane-bound enzyme protein. In intact plastids and in the total leaf extract the concentration of the enzyme protein did not change dramatically during the first 4 to 6 h of illumination. However, when the exposure to continuous white light was extended further the concentration of the enzyme protein in intact plastids began to decline rapidly while in total leaf extracts the concentration remained almost constant for the next 10 h of light. These results indicate that part of the enzyme protein may be localized outside of the plastid compartment.Abbreviations RuBPCase ribulose-1,5-bisphosphate carboxylase - SDS sodium dodecyl sulfate     

The function of proteases during the light-dependent transformation of etioplasts to chloroplasts in barley (Hordeum vulgare L.)

The role of proteolysis during the light-induced rapid decrease of the NADPH: protochlorophyllide oxidoreductase in barley was studied. A proteolytic activity with a pH optimum of 4.5 was present in a plastid preparation of etiolated barley seedlings. No other proteolytic activity could be detected. The temperature optimum for the proteolysis was 50°C, and the highest specific activity was measured with hemoglobin as the substrate. In contrast to previous proposals, no evidence for the specific involvement of this protease was found during the light-induced transformation of etioplasts to chloroplasts.