Examples ISPS Description

Figure 2-6a shows an example ISPS description and Figure 2-6b shows the corresponding VT diagram, including a loop vtbody and the ENTER operator that activates it. The ENTER operator takes as inputs values for I and DATA which are passed to the vtbody inputs for the same value. Each time the loop restarts, the current values of I and DATA are passed back to the vtbody for use in the next iteration. When the loop terminates, the final values of I and DATA are passed back to the outputs of the ENTER operator. 

In this text, iron-sulfur clusters are discussed because they appear in proteins and enzymes (1) cytochrome b(6)f, Rieske [2Fe-2S] cluster (Section 7.5 and Figure 7.26) (2) cytochrome bci, Rieske [2Fe-2S] cluster (Section 7.6 and Figure 7.30) and (3) aconitase, [4Fe-4S] cluster (Section 7.9.2.1, and Figure 7.50). The iron-sulfur protein (ISP) component of the cytochrome b(6)f and cytochrome bci complexes, now called the Rieske ISP, was first discovered and isolated by John S. Rieske and co-workers in 1964 (in the cytochrome bci complex). More information about the RISP is found in Section 7.5.1. Section 7.9.2 briefly discusses other proteins with iron-sulfur clusters—rubredoxins, ferrodoxins, and the enzyme nitrogenase. The nitrogenase enzyme was the subject of Chapter 6 in the hrst edition of this text— see especially the first edition s Section 6.3 for a discussion of iron-sulfur clusters. In this second edition, information on iron-sulfur clusters in nitrogenase is found in Section 3.6.4. See Table 3.2 and the descriptive examples discussed in Section 3.6.4. 

ISPS. In ISPS, application dependent information can be attached to any part of the description using qualifiers — lists of arbitrary attributes, with each attribute having an optional value. Qualifiers are not interpreted by the ISPS compiler instead, their interpretation is left to the application. For example, a qualifier, (time 100), may be attached to a loop to imply a maximum loop time of 100 time units. A specific application program may interpret this as a requirement that must be met. 

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