Acetyl Coenzyme A Carboxylase Activity in Developing Seedlings and Chloroplasts of Barley and Its Virescens Mutant

Abstract

Acetyl coenzyme A (CoA) carboxylase activity of whole tissue homogenates and chloroplast preparations was analyzed as the acetyl-CoA-dependent incorporation of [(14)C]bicarbonate into an acid-stable product. The absolute requirement for ATP and MgCl(2), the complete inhibition with avidin, and end-product analysis were consistent with the presence of acetyl-CoA carboxylase activity. Little difference was found between the mutant and normal tissue homogenates from the 1- to 3-day growth stages, during which period both showed a 3-fold increase. However, by 4 days, the activity of the mutant exceeded that of the normal. Fractionation studies showed that the enzyme was a soluble protein present in the stromal fraction of chloroplasts. The biotin content was also highest in the stroma, although it was found in the lamellar fraction as well. For both the mutant and the normal, the highest acetyl-CoA carboxylase activities were obtained in the stromal preparations from 4-day seedlings (54 and 31 nmoles per milligram protein per minute for the mutant and the normal, respectively) with a progressive decline by 6 and 8 days. The difference between the mutant and the normal was not due to the accumulation of an inhibitor in the normal.