Extracellular alkaline phosphatase from alveolar secretions of patients with pulmonary alveolar proteinosis.

Alkaline phosphatases in alveolar secretions from the lungs of patients with pulmonary alveolar proteinosis have been studied. A soluble form of alkaline phosphatase was isolated from the secretions and characterized. The extracellular enzyme had a pH optimum at 9.95; was stimulated by Mg2+, Ni2+, and Mn2+; was inhibited by Zn2+, Be2+, Cu2+, and low concentrations (8 mM) of L-homoarginine and imidazole; and was heat-stable at 55 degrees C. The soluble phosphatase existed primarily as a high molecular weight complex (excluded from Sepharose 4B) and could be dispersed into low molecular weight forms (205 000--285 000) by treatment with n-butanol. Following butanol treatment, the thermostability of the enzyme was markedly decreased but the kinetic properties such as the Km values, activation energies, and responses to various inhibitors were unchanged. The alkaline phosphatase may originate from unusual type 2 cells present in the alveoli of patients with pulmonary alveolar proteinosis.