UVB IRRADIATION ALTERS THE ACTIVITIES AND KINETIC-PROPERTIES OF THE ENZYMES OF ENERGY-METABOLISM IN RAT LENS DURING AGING

Ultraviolet (UV) radiation is one of the major risk factors of catarac t (loss of eye-lens transparency). The influence of UVB radiation (300 nm, 100 mu W cm(-2)) on the activity and apparent kinetic constants ( K-m and V-max) of rat lens hexokinase (HK;EC2.7.1.1), phosphofructokin ase (PFK;EC2.7.1.11), isocitrate dehydrogenase (ICDH;EC1.1.1.41) and m alate dehydrogenase (MDH;EC1.1.1.37) of energy metabolism has been inv estigated by irradiating the lens homogenate of three-and 12-month-old rats. In the three-month-old group specific activities of HK and PFK are reduced by 56 and 43 %, respectively, and there is no change in IC DH and MDH activities after a 24 h exposure. On the other hand, in the 12-month-old group the decreases are 72, 71, 24 and 16 % for HK, PFK. ICDH and MDH, respectively. UVB irradiation increases the apparent K- m of HK and PFK (in both age groups), whereas the K-m of ICDH and MDH is not altered. While the decrease in V-max of these enzymes due to UV B exposure is only marginal in three-month-old rats, it is more pronou nced (significant) in 12-month-old rats. A similar decrease in enzyme activities of HK and PFK is also observe upon UVB exposure of the inta ct rat lens. The photoinduced changes in energy metabolism may in turn have a bearing on lens transparency, particularly at an older age. (C ) 1998 Elsevier Science S.A.