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Bovine lens aldose reductase (alditol: NADP+oxidoreductase, EC 1.1.1.21) undergoes a modification induced by 2-mercaptoethanol in the presence of the redox system Fe(II)/Fe(III). The modified form (ARa) exhibits an increased hydrophobicity and tendency to aggregate. Moreover, while the native enzyme form is rather insensitive to proteolytic breakdown, the modified form is susceptible to limited proteolysis by trypsin and chymotrypsin. With both proteases, the degradation correlated with a loss of enzyme activity and results in the appearance of one molecular species of 26 KDa (for chymotrypsin) and two molecular species of 24 and 17 KDa (for trypsin). The decline in solubility and the increase in susceptibility to proteolysis of ARa suggests that the thiol-dependent metal-catalyzed modification is comparable to other oxidative systems that mark proteins for degradation.

The red emission (632 nm) of a low-power (about 10 mW) HeNe laser is used to excite liposome-bound haematoporphyrin dimethylester localized in a solid tumour implanted in the mouse leg (MS-2 sarcoma). Fluorescence from the target area, filtered at >710 nm, is converted into visible green light by means of a near-infrared-visible image converter. The photographically recorded images clearly reveal differences in fluorescence intensity of tumour tissues with respect to normal tissues. Clinical application of the procedure is proposed, and the expected advantage with respect to current fluorescence endoscopy are discussed.

The cis‐complex (IV) crystallizes in Pbca with Z = 8 and trans‐(III) in I2/a with Z = 8. An analogous cis/trans mixture (35% yield) is obtained on laser irradiation of (V) in the presence of P(O‐Me)3 in MeOH.