Evolutionary conservation of substructure architecture between yeast iso-1-cytochrome c and the well-characterized horse cytochrome c is studied with limited proteolysis, the alkaline conformational transition and global unfolding with guanidine-HCl. Mass spectral analysis of limited proteolysis cleavage products for iso-1-cytochrome c show that its least stable substructure is the same as horse cytochrome c. The limited proteolysis data yield a free energy of 3.8 6 0.4 kcal mol 21 to unfold the least stable substructure compared with 5.05 6 0.30 kcal mol The tight free energy spacing of the yeast cytochrome c substructures suggests that its folding has more branch points than for horse cytochrome c. Studies on a variant of iso-1-cytochrome c with an H26N mutation indicate that the least and most stable substructures unfold sequentially and the two least stable substructures unfold independently as for horse cytochrome c. Thus, important aspects of the substructure architecture of horse cytochrome c, albeit compressed energetically, are preserved evolutionally in yeast iso-1-cytochrome c.

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Union Carbide Y-12 Development D i v i s i o n I n s t r u m e n t a t i o n and C h a r a c t e r i z a t i o n Department Post O f f i c e Box Y, Oak Ridqe, Tennessee 37830 A b s t r a c t A new, easy t o operate, p u l s e -t i m i n g d i s -T h i s instrument combines c r i m i n a t o r has been developed f o r p r o d u c t i o n i n s p e c t i o n o f p a r t s . t h e noise-blanking advantages o f t h r e s h o l d d i s c r i m i n a t i o n w i t h t h e echo-timing p r e c i s i o n o f zero-crossing d i s c r i m i n a t i o n by u s i n g a shaped t h r e s h o l d d e t e c t o r o u t p u t t o enable a zero-crossing d i s c r i m i n a t o r o n l y when t h e RF u l t r a s o n i c s i g n a l exceeds an a d j u s t a b l e threshold. F l i p -f l o p s a r e then used t o separ a t e t h e echoes. a 30-dB amplitude change o f a 5-MHz transducer waveform i s o n l y 200 psec, w h i l e t i m i n g j i t t e r i s o n l y 30 psec. 100 psec. t i m i n g e r r o r corresponds t o an e r r o r o f 0.64 micrometer i n aluminum. s e l e c t i o n system c o r r e c t s f o r p u l s e p o l a r i t y i n v e r s i o n s . A time-to-pulse-height c o n v e r t e r a l l o w s o p e r a t i o n as a B-scan instrument capable o f d e t e c t i n g flaws a t depths o f 0.25 mn i n a1 umi num. D i s c r i m i n a t o r t i m i n g walk f o r Long-term t i m i n g s t a b i l i t y i s I n thickness gaging, a 200-psec An automatic p o l a r i t y 1. I n t r o d u c t i o n There i s a need f o r a high-speed, p r e c i s i o nt i m i n g instrument f o r u l t r a s o n i c i n s p e c t i o n o f p r e c i s i o n p a r t s , easy-to-use d i s p l a y o f B-scan data t o g i v e a p i c t u r e o f p a r t defects. instruments a r e too slow t o o b t a i n d e s i r e d measurement accuracy and r e q u i r e s u b s t a n t i a l o p e r a t o r s k i l l . The many i n t e r c o n n e c t i o n s on comnercial u n i t s a l s o l i m i t accuracy, s i n c e highspeed p u l s e -t i m i n g measurements a r e very s e n s i t i v e t o c a b l e l e n g t h ; i.e., a 20-cm d i f f e r e n c e i n c a b l e l e n g t h w i l l cause a t i m i n g e r r o r o f 1 nanosecond (nsec). Thus, high-speed, s e l f -c o n t a i n e d i n s t r u m e n t a t i o n t h a t i s easy t o use i s needed f o r p r o d u c t i o n i n s p e c t i o n o f p a r t s . There i s a l s o a need f o r an Comnercially a v a i l a b l e 2. Theory o f Operation flaws o r measure thicknesses by r e f l e c t i o n s o f sound waves o f f o f d e f e c t s and surfaces. I n a conventional pulse-echo gage, an u l t r a s o n i c transducer i s e x c i t e d by a h i g h -v o l t a g e pulse. The v o l t a g e causes t h e resonant c r y s t a l t r a n sducer t o v i b r a t e , thereby generating t h e U l t r a s o n i c sound can be u t i l i z e d t o d e t e c t u l t r a s o n i c pulse. specimen as i l l u s t r a t e d i n Figure 1. p u l s e h i t s a specimen's f r o n t surface, p a r t o f t h e p u l s e ( f i r s t ech...

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