Ca2+ is a cofactor required for membrane transport and maturation and is a yield-determining factor in high cell density penicillin amidase production.
Penicillin amidases (PAs) from E. coli and A. faecalis are periplasmic enzymes that contain one tightly bound Ca(2+) per molecule that does not directly participate in the enzymatic function. This ion may, however, be required for the maturation of the pre-pro-enzyme. The pro-enzyme of homologous PAs are translocated through the Tat- (E. coli PA(EC)) and Sec- (A. faecalis PA(AF)) transport systems, respectively. Cell fractionation, electrophoresis, immunoblotting, and activity staining demonstrated that Ca(2+) binding is required for the membrane transport and maturation of the pro-enzyme to active enzyme. Pro-enzyme without Ca(2+) was targeted to the membrane but not translocated. Influence of Ca(2+) in medium and feed was studied for high cell density cultivations of E. coli expressing these enzymes. Without Ca(2+) in the feed the synthesis of the pre-pro-enzyme was hardly influenced. At optimal Ca(2+) content in the feed the active enzyme amount could be increased by 2 orders of magnitude up to 0.9 g/L (PA(EC)) and 2.3 g/L (PA(AF)) or 4% (PA(EC)) and 8% (PA(AF)) of the cell dry weight. The corresponding specific activities are 1700 U (PA(EC)) and 14000 U (PA(AF)) per gram cell dry weight, respectively. These values are higher than those published previously. Thus, for optimal yields of the studied and other extra- and periplasmic enzymes that require Ca(2+) or other ions as cofactors for membrane transport and maturation, sufficient cofactor must be added in the feed.
Kasche
Volker
V
Biotechnologie I and II, Technische Universität Hamburg-Harburg, Denickestrasse 15, 21071 Hamburg, Germany. volker.kasche@t-online.de
Ignatova
Zoya
Z
Märkl
Herbert
H
Plate
Wilhelm
W
Punckt
Nils
N
Schmidt
Dorothea
D
Wiegandt
Katharina
K
Ernst
Burkhard
B
D042481:Alcaligenes faecalis / Q000201:enzymology / Q000254:growth & development; D019149:Bioreactors; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D010399:Penicillin Amidase / Q000096:biosynthesis* / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000302:isolation & purification
D014874:Water Pollutants, Chemical; D010399:Penicillin Amidase; D002118:Calcium