STUDY OF BIOGENESIS AND SECRETION OF ALKALINE-PHOSPHATASE AND ITS MUTANT FORMS IN ESCHERICHIA-COLI .3. SUBSTITUTIONS OF ALKALINE-PHOSPHATASE N-TERMINAL AMINO-ACID AFFECT ENZYME BIOGENESIS

The effect of N-terminal amino acid substitutions in the Escherichia c oli alkaline phosphatase [EC 3.1.3.1] on its biogenesis was studied. U sing E. coli strains carrying different amber suppressors and the phoA gene with an amber mutation at position corresponding to the N-termin al amino acid in mature protein, Arg(+1) was changed to Ser, Gin, Tyr, Leu, Gly, Ala, Glu, Phe, His, Cys, Lys, or Pro. All these amino acid substitutions do not prevent secretion and formation of active enzyme. However, introduction of Pro in position +1 completely inhibits signa l peptide cleavage (processing) and results in accumulation of the pre cursor inside the cells. Other amino acid substitutions have no effect on processing. All N-terminal amino acid substitutions studied change the alkaline phosphatase isozyme spectrum. The experimental evidence obtained suggests that the protease splits off the alkaline phosphatas e N-terminal arginine is ineffective with Glu and Lys at position +1.