Three xylanases produced inductively by methyl β-xyloside from ]itStreptomyces sp. No. 3137 were purified to homogeneity. Rabbit antisera against two xylanases, X-I and X-II-B, were prepared.
In double diffusion experiments, antiserum to X-I (anti-I serum) and antiserum to X-II-B (anti-II-B serum) formed a precipitation band with X-I, and X-II-B, respectively. No immunoprecipitate, however, was observed when xylanase X-II-A or X-II-B was tested against anti-I serum, and when X-I was done against anti-II-B serum. Anti-II-B serum formed a line of identity between X-II-A and X-II-B. The data indicate that X-II-A and X-II-B are closely related in immunology, while X-I is distinct.
The amino terminals were an alanine residue for X-I and threonine residues for X-II-A and X-II-B by the dansyl chloride method. The carboxyl terminals were an aspartic acid residue for X-I and an alanine residue for X-II-B by carboxypeptidase Y method.
Amino acid analysis showed that X-II-A and X-II-B had a large amount of glutamic acid and alanine residues, and a small amount of tyrosine, threonine, and serine residues compared with X-I.

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