Alkaliphilic Bacillus sp. S-1 secretes a large amount (approximately 80% of total pullulanase activity) of an extracellular pullulanase (PUL-E). The pullulanase exists in two forms: a precursor form (PUL-I: $M_r$ 180,000), and a processed form (PUL-E: $M_r$ 140,000). Two forms were purified to homogeneity and their properties were compared. PUL-I was different in molecular weight, isoelectric point, $NH_2$-terminal amino acid sequence, and stabilities over pH and temperature ranges. The catalytic activities of PUL-I were also distinguishable in the $K_m$ and $V_{max}$ values for various substrates, and in the specific activity for pullulan hydrolysis. PUL-E showed 10-fold higher specific activities than PUL-I. However. PUL-I is immunologically identical to PUL-E, suggesting that PUL-I is initially synthesized and proteolytically processed to the mature form of PUL-E. Processing was inhibited by PMSF, but not by pepstatin, suggesting that some intracellular serine proteases could be responsible for processing of the PUL-I. PUL-I has a different conformational structure for antibody recognition from that of PUL-E. It is also postulated that the translocation of alkaline pullulanase(AP) in the bacterium possibly requires processing of the $NH_2$-terminal region of the AP protein. Processing of the precursor involves a conformational shift. resulting in a mature form. Therefore. precursor processing not only cleaves the signal peptide, but also induces conformational shift. allowing development of active form of the enzyme.