Ocular lens NAD kinase: partial purification and metabolic implications.

The ocular lens displays a significant amount of NADP(H) dependent metabolic traffic, but the origin of this cofactor has not been established. Size exclusion chromatography of bovine lens crude extract on a Sephacryl S300-HR column fitted with an eluate concentrator revealed two bands with NAD kinase activity, based on enzymatic cycling with signal amplification of the column fractions using a Cobas-Fara II centrifugal fast analyzer. Ve/Vo ratios from the chromatographic runs suggest that the relative molecular weight values lie within the ranges 8.91-3.98 x 10(5) and 2.04-1.26 x 10(5), respectively, for these two bands. An approximately 10-fold enhancement of enzyme activity over the crude fraction is realized from the chromatography step. Results point to NAD kinase as the source generator of this anchoring and linking cofactor for the oxidative stress and pentose phosphate enzyme systems, respectively.