J. Biochem, 1976, Vol. 80, No. 2 379-387
© 1976 Japanese Biochemical Society
research-article |
The Structure of a Glycopeptide (GP-II) Isolated from Rhizopus Saccharogenic Amylase1,2
Laboratory of Microbial Ecology, The Institute of Physical and Chemical Research Wako, Saitama 351
Mild alkaline treatment of glycopeptide (GP-II) resulted in the loss of 1 mole of serine and 5 moles of threonine per mole of GP-II, suggesting the presence of O-glycosyl bonds between 1 serine and 5 threonine residues and carbohydrate chains.
Treatment of GP-II with alkaline borohydride released only disaccharide. Methylation studies of the carbohydrate moiety gave 2, 3, 4, 6-tetra-O-methyl and 2, 4, 6-tri-O-methyl derivatives of mannose in a ratio of approximately 1 : 1. In addition, one step of Smith degradation resulted in the loss of about 6 residues of mannose per mole of GP-II. Moreover, 
-mannosidase [EC 3. 2. 1. 24] liberated about 6 residues of mannose per mole of GP-II. On the basis of these data, the structure of the carbohydrate moiety of GP-II was confirmed to be 3-O--mannosylmannose.
The amino- and carboxyl-terminal amino acids of GP-II were determined to be threonine and serine, respectively. On reductive cleavage of N-proline bonds with metallic sodium in liquid ammonia, 2 moles of alanine per mole of GP-II were lost. From the compositions of three fragments isolated from the reductive cleavage products, the amino acid sequence of the peptide portion of GP-II was determined.
Based on these data, a probable structure was proposed for GP-II.
1 This work was supported in part by a research grant for "Studies on Life Sciences" from the Institute of Physical and Chemical Research.
This paper is Part V in the series "Studies on Saccharogenic Amylase from Rhizopus javanicus." Part IV appeared in Agr. Biol. Chem. (1975) 39, 1711—1717.