Table I.

First generation variant activity and stability

Variant no.	% of pH 6.0 activity relative to OPT	% of pH 4.5 activity relative to OPT	Time enzyme remains active in presence of pepsin and pH 4.5 buffer
6609	0	0	−
6610	0	0	−
6611	49	98	−
6613	66	67	−
6614	97	79	−
6615	48	59	−
6617	30	70	−
6618	161	184	−
6619	156	158	−
6620	90	89	−
6621	61	64	−
6622	103	89	−
6623	125	119	−
6626	105	119	−
6627	93	81	−
6628	131	143	−
6629	85	106	−
6630	47	62	−
6631	155	150	+
6633	51	39	+
6634	77	60	−
6635	62	60	−
6636	99	93	−
6637	32	77	−
6638	76	153	−
6639	88	56	−
6641	69	89	−
6643	61	80	?
6644	108	102	−
6645	8	10	−
6646	101	95	+
6647	122	114	−
6648	40	60	−
6649	101	87	−
6650	34	60	−
6651	67	68	−
6652	94	122	−
6653	87	98	+
6654	80	53	+
6655	48	95	−
6656	122	128	+

Assays were performed under the three conditions of pH 6.0, pH 4.5 and pepsin + pH 4.5. ×10 enzyme was used in the pepsin assay compared with the pH 6.0 and pH 4.5 assays. pH 6.0 and pH 4.5 data are given as relative percentages of wild-type SC PEP activity at the same condition (variant activity/wild-type activity × 100). For the pepsin assay, results are reported as the duration for which the enzyme retains activity. (−) represents an enzyme remaining active for<2 min, (+) represents an enzyme retaining activity for 2–5 min, (++) represents an enzyme retaining activity for 5–9 min, and (+++) represents an enzyme retaining activity for >9 min. For reference, wild-type SC PEP remained active for <1 min (41 of the 47 first generation variant activity values are listed in this table due to prior analysis by a different method for the remaining six). (?) implies not determined.