Cataract in a diabetic patients is because of accumulation of sorbital in lens. The enzyme responsible for this is
First, I remember that in diabetes, high glucose levels lead to the polyol pathway being activated. The key enzymes here are aldose reductase and sorbitol dehydrogenase. Aldose reductase converts glucose to sorbitol, and then sorbitol dehydrogenase converts sorbitol to fructose. But in the lens of the eye, the problem is that sorbitol accumulates because the lens can't excrete it. This leads to osmotic stress, swelling, and cataracts.
So the enzyme responsible for the initial step, converting glucose to sorbitol, is aldose reductase. The options probably include aldose reductase as the correct answer. The other enzymes might be things like hexokinase, glucose-6-phosphatase, or maybe sorbitol dehydrogenase. Wait, sorbitol dehydrogenase converts sorbitol to fructose, but if that's the case, then if it's deficient, sorbitol would accumulate. But in diabetes, the issue is excess glucose being converted to sorbitol via aldose reductase. So the main problem here is the overactivity of aldose reductase, not a deficiency. Therefore, the correct enzyme is aldose reductase.
Now, the wrong options: Hexokinase is involved in the first step of glycolysis, converting glucose to glucose-6-phosphate. Glucose-6-phosphatase is part of gluconeogenesis and glycogenolysis. Sorbitol dehydrogenase is the next enzyme in the pathway but isn't responsible for the accumulation in this case. So the correct answer is aldose reductase.
For the clinical pearl, it's important to remember that aldose reductase inhibitors are a potential treatment for diabetic cataracts, though they aren't widely used. Also, the polyol pathway's role in diabetic complications like neuropathy and retinopathy is similar, all due to sorbitol accumulation. That's a key point for exams.
**Core Concept**
Diabetic cataracts result from sorbitol accumulation in the lens due to the polyol pathway. Elevated glucose is reduced to sorbitol by aldose reductase, which cannot be efficiently excreted, causing osmotic swelling and lens damage.
**Why the Correct Answer is Right**
Aldose reductase catalyzes the first step of the polyol pathway, converting glucose to sorbitol. In hyperglycemia, this enzyme becomes overactive, leading to intracellular sorbitol accumulation in the lens. Sorbitol cannot cross cell membranes, causing osmotic stress, edema, and eventual cataract formation. This mechanism is central to diabetic complications like neuropathy and retinopathy as well.
**Why Each Wrong Option is Incorrect**
**Option A:** Hexokinase phosphorylates glucose to glucose-6-phosphate in glycolysis, not sorbitol metabolism.
**Option B:** Glucose-6-phosphatase is involved in gluconeogenesis and glycogenolysis, unrelated to sorbitol accumulation.
**Option C:** Sor