Molecular Biology of Extracellular Enzymes

Abstract

Publisher Summary This chapter discusses the process of secretion of enzymatic and nonenzymatic proteins (for example, binding proteins) in both gram-positive and gram-negative bacteria. The chapter examines the increasing evidence that indicates that these secretory proteins are synthesized from membrane-bound polyribosomes in precursor form and are secreted directly through the membrane as they are being synthesized. The identification of cytoplasmic enzymes released by lysis versus true extracellular enzymes is performed by determination of the cytoplasmic versus medium level of the particular enzyme during growth of the bacteria, and demonstration of the lack of release of other cytoplasmic enzymes. It has been discovered that the membrane-bound form of penicillinase has phosphatidic acid covalently bound to the serine of its amino terminal end. Because the other amino acids of the peptide are hydrophilic, it is the acyl fatty acids of the phosphatidylserine-penicillinase, which enable the hydrophobic binding of the precursor form of penicillinase to the cytoplasmic membrane, and presumably assists its secretion through the cytoplasmic membrane.