primary structure is meant its amino acid sequence. By its tertiary structure is
meant the way it likes to "fold up". The point is that enzymes don't like
being in straight lines, as we have so far exhibited them. At each internal
amino acid (all but the two ends), there is a possibility of a "kink", which is
dictated by the letters in the corners. In particular, 'l' and 'r' stand for
"left" and "right", and's' stands for "straight". So let us take our most
recent sample enzyme, and let it fold itself up to show its tertiary structure.
We will start with the enzyme's primary structure, and move along it from
left to right. At each amino acid whose corner-letter is 'l' we'll put a left
turn, for those with 'r', we'll put a right turn, and at's' we'll put no turn. In
Figure 88 is shown the two-dimensional conformation for our enzyme.cop1l'SWI ¢: cut ¢: mvl ¢: int1l'
mvr1l'
rpy =? Ina =? rpuFIGURE 88. The tertiary structure of a typoenzyme.Note the left-kink at "rpu", the right-kink at "swi", and so on. Notice also
that the first segment ("rpy ~ ina") and the last segment ("swi ~ cop") are
perpendicular. This is the key to the binding-preference. In fact, the
relative orientation of the first and last segments of an enzyme's tertiary structure
determines the binding-preference of the enzyme. We can always orient
the enzyme so that its first segment points to the right. If we do so, then the
last segment determines the binding-preference, as shown in Figure 89.
FIGURE 89. Table of binding-preferences for typoenzymes.First Segment Last Segment Binding-letter=? =? A=? 1l' c
=? ,JJ G=? <= TSelf-Ref and Self-Rep^511