Here's some papers to check out:
Hall, B. G. and T. Zuzel (1980) Evolution of a new enzymatic function by recombination within a gene. Proceedings of the National Academy of Science USA 77(6): 3529-33.
Clarke, P. H. (1980) "Experiments in microbial evolution: new enzymes, new metabolic activities" Proc. R. Soc. Lond. B 207: 385-404. (good review)
Hall, B. G. (1983) "Evolution of new metabolic functions in laboratory organisms" Evolution of genes and proteins
Ohno, S. (1984) "Birth of a unique enzyme from an alternative reading frame of the pre-existed, internally repetitious coding sequence", Proc. Natl. Acad. Sci. USA, Vol. 81, pp. 2421-2425
Lin, E.C.C., & Wu, T.T. (1984) Functional divergence of the L-Fucose system in Escherichia coli. In R.P. Mortlock (ed.), "Microorganisms as Model Systems for Studying Evolution" Plenum, New York.
Hartley, B.S. (1984), Experimental evolution of ribitol dehydrogenase. In R.P. Mortlock (ed.), "Microorganisms as Model Systems for Studying Evolution" Plenum, New York.
Prijambada ID et al., 1995. Emergence of nylon oligomer degradation enzymes in Pseudomonas aeruginosa PAO through experimental evolution. Applied and Environmental Microbiology 61(5): 2020-2022.
Papadopoulos, D., Schneider, D., Meier-Eiss, J., Arber, W., Lenski, R. E., Blot, M. (1999). Genomic evolution during a 10,000-generation experiment with bacteria. Proc. Natl. Acad. Sci. U. S. A. 96: 3807-3812
Zhang, J., Y.-P. Zhang and H. F. Rosenberg, 2002. Adaptive evolution of a duplicated pancreatic ribonuclease gene in a leaf-eating monkey. Nature Genetics 30: 411-415.