The α‐Amylolysis of Starch

Models for depolymerizing enzymes. Application to α‐amylases

“…The degree of repetitive attack, 3.4, for porcine pancreatic a-amylase determined by Banks et al5 (see Table 11) roughly agrees with the value of 3.8 measured by Robyt and F r e n~h .~ I believe that the enzymic method used by Banks et al to estimate the number of chains in the digest probably underestimates the number of chains and thereby underestimates 0. As these authors noted, their method for determining the average chain length is only valid when there is no preferential build-up on salivary amylase, the ratios of even-and odd-member oligosaccharides for chain length [1][2][3][4][5][6]. These ratios are shown in Table 111.…”

“…VinklO established that a plot of the reciprocal of the average chain length versus time is linear for a random hydrolytic process. Greenwood et al 6,839 found that 1/DP, versus time was linear for every endo-amylase that they examined and concluded that the first encounter of the enzyme with the substrate must occur a t random. However, Robyt and French3 have noted that DP, is not sensitive to the presence of oligosaccharides generated by repetitive attack so that a plot of 1/DP, versus time will be insensitive to repetitive attack.…”

“…Banks (personal communication) has independently arrived at the same conclusions. Greenwood et al6,8,9 employed the procedure of Vink to demonstrate that the initial cleavage by amylases on large substrates occurs at random. VinklO established that a plot of the reciprocal of the average chain length versus time is linear for a random hydrolytic process.…”

“…The retained fragment suffers reattack one or more times near a chain terminus during the lifetime of the enzyme substrate-fragment complex. Finally, the substrate-fragment dissociates from the e n~y m e .~ Greenwood et al [5][6][7][8][9] have argued that the preferential hydrolysis of bonds near chain ends can account for the large amounts of oligosaccharides observed in the amylase digests (see Fig. lc).…”

“…amyloliquefaciens) amylase is unique among the enzymes tested because it does not repetitively attack substrate fragments. Greenwood et al6,8,9 employed the procedure of Vink to demonstrate that the initial cleavage by amylases on large substrates occurs at random. VinklO established that a plot of the reciprocal of the average…”