Table 1.

Complexity of the AA receptor repertoire

CategoryChain length
234568
Response properties of glomeruli
 1rttttt
 2nrtttt
 3nnnrtt
 4nnnnrt
 5nnnnnr
nNH2β-OH
 6tt
 7tn
 8rn
 9nt
10nn
  • Categories of AA-responsive glomeruli based on differential tuning properties of individual glomeruli. Top: r, required minimal chain length; t, tolerated (all other chain lengths leading to activation); n, no response (compound is not sufficient for activation). Five different tuning properties were found in this analysis. Bottom: influence of functional groups in the AA side chain; r, required (presence of functional group is required); t, tolerated (response in presence and absence of functional group); n, not tolerated (functional group needs to be absent for response). Note that not all possible combinations exist. Five different tuning categories were found for functional groups. At least some are further subdivided because of different dependence on chain length (see Fig. 8). The maximal possible number of 5 × 5 categories is not reached, however, because not all combinations of chain-length preference and functional-group preference are realized (e.g., category 4 may be subdivided by categories 7, 8, and 10, but is mutually exclusive with categories 6 and 9). The total number of categories represents a minimal estimate for the total number of different receptors.