Table 4.

Distribution of average packing values in helical membrane and soluble proteins^*

Position‡	Membrane proteins		α-Bundle proteins†		α-Nonbundle proteins†		αβ proteins†
	Packing value	Occurrence (%)	Packing value	Occurrence (%)	Packing value	Occurrence (%)	Packing value	Occurrence (%)
≤0.3 (exposed)	0.250	15.61	0.234	24.17	0.231	23.48	0.228	29.26
>0.3–0.55 (interm.)	0.432	68.28	0.431	58.37	0.437	61.45	0.419	56.05
>0.55 (buried)	0.598	16.11	0.590	17.46	0.591	15.07	0.591	14.69

^*The occluded surface calculations were carried out on full protein structures, but the packing values reported represent the helical residues only. 

^†The soluble proteins were classified according to Michie et al. (26). 

^‡See text.